User uday - MathOverflow most recent 30 from http://mathoverflow.net 2013-06-18T06:34:29Z http://mathoverflow.net/feeds/user/7333 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/96504/pseudo-differential-operators-which-are-independent-of-lower-order-perturbations Pseudo-differential operators which are independent of lower order perturbations Uday 2012-05-09T20:03:00Z 2013-06-11T22:22:00Z <p>In the area of pseudo-differential operators, we know that for elliptic type or real principal type operators reductions are independent of lower order terms. For example, if $P$ is zeroth order real principal type operator with principal symbol $q(x,\xi),$ then for a lower order perturbation $R$ we can always find a zeroth order elliptic operator $E$ such that $E^{-1}(P+R)E=q(x,D).$ </p> <p>The reason for this independence of lower terms in elliptic type operator is because the principal term can be inverted and in real principal type operator is there exists a non-degenerate Hamiltonian flow. </p> <p>Are there any other class of pseudo-differential operators which have this property? If not, is there any work in microlocal analysis which tells us that elliptic and real principal type operators form the largest such class? </p> <p>Note: As stated in the question, my interest is in 'reductions of operators', i.e., transforming to simpler forms. I am not interested in regularity or solvability problems of pseudo-differential operators. I am aware of examples(not stated in the question) of operators for which the solvability issues are independent of lower order terms. For instance, <a href="http://annals.math.princeton.edu/wp-content/uploads/annals-v163-n2-p02.pdf" rel="nofollow">http://annals.math.princeton.edu/wp-content/uploads/annals-v163-n2-p02.pdf</a></p> http://mathoverflow.net/questions/88750/functions-satisfying-one-one-iff-onto functions satisfying "one-one iff onto" Uday 2012-02-17T19:00:00Z 2013-03-22T01:03:09Z <p>Hello Everybody. </p> <p>I need some more examples for the following really interesting phenomenon:</p> <pre><code> A function from the class ... is one-one iff it is onto. </code></pre> <p>Some examples I know:</p> <p>1) Finite set case: functions from $\lbrace 1,2,\dots,n\rbrace$ to itself is one-one iff onto.</p> <p>2) Linear operators $T\colon V\rightarrow V,$ where $V$ is a finite-dimensional vector space is also one-one iff onto.</p> <p>3) Linear operators of the from (I-K) where K is some compact operator acting on a Banach space satisfies this property. This is the famous result of Fredholm. </p> <p>It is very easy to find domains where the result fails. </p> <p>I remember my teacher telling me that 'compactness is the next best thing to finiteness', hence this result which trivially holds in the finite case can happen only in the compact setting. I would like to know, if this is really the case or are there any other examples? </p> <p>Thank you in advance. </p> <p>EDIT: Looking at some answers, I thought it is better if the scope of the question is broadened. </p> <p>Does injection (surjection) imply surjection (injection) and isomorphism/isometry? (i.e. by assuming one-one can I get ontoness and structure preserving properties free)</p> http://mathoverflow.net/questions/117263/optimization-version-of-the-sylvester-equation Optimization version of the Sylvester equation Uday 2012-12-26T15:40:29Z 2012-12-27T11:25:42Z <p>The <a href="http://en.wikipedia.org/wiki/Sylvester_equation" rel="nofollow">Sylvester equation</a> is a matrix equation of the form $AX-XB=C,$ where $A,B,C$ are given matrices of dimension $m\times m,n\times n$ and $m\times n$ and $X$ is an unknown matrix of dimension $m\times n.$ It is a well known fact that the equation has an unique solution if and only if the matrices $A$ and $B$ have disjoint spectrum. If they do not have disjoint spectrum, then the result in general depends on $C.$ </p> <p>While determining perturbation of eigenvalues in certain context I was naturally drawn to the the problem of determining the minimum, $min_{X}||AX-XB-C||,$ where $||.||$ is the <a href="http://en.wikipedia.org/wiki/Matrix_norm#Frobenius_norm" rel="nofollow">Frobenius norm</a>. Clearly, if the spectrum of $A$ and $B$ is disjoint then there is a choice of $X$ for which the norm is zero. Otherwise, we need to resort to certain optimization techniques. One approach could be to vectorize the matrices using Kronecker products and determine the minimum of a linear system. </p> <p>The problem is: "What is the choice of $X$ for which the norm $||AX-XB-C||$ attains minimum (if it exists) when the spectra of $A$ and $B$ are not disjoint?" </p> <p>I have not found any literature on discussion about similar problems. I would be very thankful for any references or suggestions in this direction. </p> http://mathoverflow.net/questions/90839/grothendieck-on-topological-vector-spaces Grothendieck on Topological Vector Spaces Uday 2012-03-10T18:28:39Z 2012-12-19T10:46:35Z <p>In the short biography article on the Alexander Grothedieck</p> <p><a href="http://www.ams.org/notices/200409/fea-grothendieck-part1.pdf" rel="nofollow">http://www.ams.org/notices/200409/fea-grothendieck-part1.pdf</a> ,</p> <p>it is mentioned that after Grothendieck submitting his first thesis on Topological Vector Spaces(TVS), apparently, told Bernard Malgrange that 'There is nothing more to do, the subject is dead.' </p> <p>Also, after nearly two decades, while listing 12 topics of his interest Grothendieck gives least priority to Topological Tensor Products and Nuclear Spaces.</p> <p>Now, the questions I have are:<br> What made Grothendieck make this pronouncement on TVS? Could somebody indicate some significant problems or contributions in this area after Grothendieck? My interest is not in the applications or the impact on the subject on other areas of mathematics but I am interested in knowing about the growth of TVS theory itself. </p> <p>Thank you, in advance, for your answer. </p> http://mathoverflow.net/questions/116150/triangularizing-a-function-matrix-with-smooth-eigenvlaues Triangularizing a function matrix with smooth eigenvlaues Uday 2012-12-12T06:45:30Z 2012-12-12T10:55:31Z <p>Given a matrix with function entries, which are smooth and homogeneous, and having smooth eigenvalues, can we find a conjugating matrix with smooth and homogeneous entries that triangularize the given matrix? For instance, given $A(x)$ is an $N\times N$ matrix with entries $a_{ij}(x)$ that are smooth and homogeneous in $x$ of order $1.$ Also, given that the eigenvalues of $A(x)$ are smooth. Find an invertible(may be in small neighborhood) matrix $E(x)$ with smooth entries such that $E^{-1}(x)A(x)E(x)$ is upper-triangular. </p> <p>Sometime back I had asked a question on <a href="http://mathoverflow.net/questions/96902/triangularizing-a-matrix-with-function-entries" rel="nofollow">triangularizing a function matrix</a>. Now, it is clear to me that it is possible to find, by Schur decomposition, a triangularizing matrices which are measurable. Also, one of the answers posted for that question was, it is not always possible to uniformly triangularize especially for certain matrices with non-differentiable eigenvalues. The question in this post is directed towards smoothness and homogenity of such matrices under the condition that they have smooth eigenvalues. </p> <p>I would be grateful for any reference or insight in this direction. Thank you. </p> http://mathoverflow.net/questions/111915/a-question-about-first-order-hyperbolic-equations a question about first-order hyperbolic equations Uday 2012-11-09T16:37:44Z 2012-11-09T19:33:47Z <p>Performing certain manipulations on pseudo-differential equations I have come across the following first order equation: $$D_{t}u-\lambda(t,x,D_{t},D_{x})u=0, \ \ (*)$$ where $\lambda$ is a scalar pseudo-differential operator with the principal symbol being real-valued and independent of $D_{t}.$ But, the lower-order terms of $\lambda$ depend on $D_{t}$ (or $\tau$ at the symbol level). </p> <p>I was expecting a hyperbolic equation. But, I find that standard text books(like M.Taylor's 'Pseudo-differential operators') treat only equations in which $\lambda$ term is independent of $D_{t}$ (or $\tau$ at the symbol level). </p> <p>For the equation $(*)$ to be hyperbolic, is it necessary that $\lambda$ to be independent of $D_{t}$? Are there any references which discuss these issues? </p> http://mathoverflow.net/questions/97296/second-order-operator-with-real-coefficients-and-not-locally-solvable second order operator with real coefficients and not locally solvable Uday 2012-05-18T10:39:23Z 2012-09-27T18:46:26Z <p>This question is a follow up of the following answer I posted recently: </p> <p><a href="http://mathoverflow.net/questions/68680/counterexamples-in-pde/97250#97250" rel="nofollow">http://mathoverflow.net/questions/68680/counterexamples-in-pde/97250#97250</a></p> <p>Is there a second order partial differential operator with <strong>real</strong> coefficients which are not solvable in <a href="http://en.wikipedia.org/wiki/Lewy%27s_example" rel="nofollow">Lewy sense</a>? I am also not aware of first and third order operators but I thought second order operator is a natural question as we may be able to apply some conjugations of known first order non-solvable Lewy like operators with complex coefficients. In this direction, Mizohata's example $\frac{\partial }{\partial x}+ix\frac{\partial }{\partial y}$ was not helpful as it is giving me Grushin like operators whose solvability is proved. </p> http://mathoverflow.net/questions/97296/second-order-operator-with-real-coefficients-and-not-locally-solvable/108274#108274 Answer by Uday for second order operator with real coefficients and not locally solvable Uday 2012-09-27T18:46:26Z 2012-09-27T18:46:26Z <p>The following example is an second order differential operator with real coefficients defined on $\mathbb{R}^{3}$ which is not solvable about origin:</p> <p>$Pu=(x_{2}^{2}-x_{3}^{2})D_{1}^{2}u+(1+x_{1}^{2})(D_{2}^{2}u-D_{3}^{2}u)-$ $$x_{1}x_{2}D_{1}D_{2}u-D_{1}D_{2}(x_{1}x_{2}u)+x_{1}x_{3}D_{1}D_{3}u+D_{1}D_{3}(x_{1}x_{3}u)$$</p> <p>This beautiful operator was given by H$\ddot{o}$rmander in his Springer 1963 'Linear Partial Differential Operators' book. </p> http://mathoverflow.net/questions/105824/what-is-the-non-intuitive-part-in-sphere-eversion-turning-inside-out What is the 'non-intuitive' part in sphere eversion (turning inside out)? Uday 2012-08-29T12:25:38Z 2012-08-29T13:12:57Z <p>Hello, Everybody!</p> <p>The question does not mean sphere eversion is intuitive to me! In fact, it is just the opposite and that is the purpose of this question. </p> <p>Recently, I was reading about <a href="http://en.wikipedia.org/wiki/Smale%27s_paradox" rel="nofollow">Smale's paradox</a>, the problem of sphere eversion (turning a sphere inside out). The wiki article is quite clear and gave me a good overview of the topic. I happened to see an animation of the eversion process as well. </p> <p>The problem of sphere eversion is to construct a homotopy between the inside and outside of a sphere in a three dimensional space. During the continuous deformation self-intersections of the sphere are allowed and creating creases is not allowed. </p> <p>Given that we can self-intersect the sphere while the process of eversion what could be a possible obstruction to the eversion? What exactly do we mean by self-intersection? Moreover, I find it difficult to imagine why a similar process cannot be employed in the circle case? Why can't we self intersect a circle with itself to turn it inside out? Is there an easy explanation for this phenomenon? </p> <p>This topic is new to me. I hope the question is not too naive. Thank you in advance. </p> http://mathoverflow.net/questions/105021/why-take-complex-powers-of-pseudo-differential-operators Why take 'complex powers' of pseudo-differential operators? Uday 2012-08-19T05:21:52Z 2012-08-19T07:30:08Z <p>Given a pseudo-differential operator $P$ of order zero, <a href="http://cdsweb.cern.ch/record/469079/" rel="nofollow">Seeley</a> showed that the holomorphic family of operators $\lbrace P^{z} : z\in \mathbb{C} \rbrace$ of all complex powers is contained in the class of pseudo-differential operators. </p> <p>Apart from knowing that we can take powers of these operators, is there any application of this theory? I understand the utility of raising operators to fractional powers. But, irrational and complex powers are not clear. </p> http://mathoverflow.net/questions/98126/why-is-symplectic-geometry-so-important-in-modern-pde/98132#98132 Answer by Uday for Why is symplectic geometry so important in modern PDE ? Uday 2012-05-27T16:57:41Z 2012-05-27T17:02:59Z <p>Fourier Integral Operator is an operator which has its Schwartz kernel as a distribution whose singularities are on a Lagrangian submanifold. In fact, we can associate a FIO with an amplitude and a Lagrangian submanifold in a unique manner. Lagrangian submanifold is a topic of symplectic geometry.</p> http://mathoverflow.net/questions/59086/motivation-for-and-history-of-pseudo-differential-operators/97591#97591 Answer by Uday for Motivation for and history of pseudo-differential operators Uday 2012-05-21T18:52:48Z 2012-05-21T19:50:19Z <p>A slightly different motivation for fourier integral operators and pseudo-differential operators is given in the first chapter of this <a href="http://books.google.co.in/books?id=Zi1UzHg64xsC&amp;pg=PA1&amp;lpg=PA1&amp;dq=mathematics+past+and+present+fourier+integral+operators&amp;source=bl&amp;ots=uuKfr0Seuj&amp;sig=Oz86sY8Ow8GdCQw7A5Dp_kslIII&amp;hl=en&amp;sa=X&amp;ei=S4q6T6S7F4nMrQfQiNXYBw&amp;ved=0CGMQ6AEwAg#v=onepage&amp;q=mathematics%2520past%2520and%2520present%2520fourier%2520integral%2520operators&amp;f=false" rel="nofollow">book</a>. In this chapter, V.Guillemin presents this subject from the conormal bundles point of view and then shows how pseudo-differential operators are a special case of operators coming out of the Fourier distributions. </p> <p>Section 3 of this chapter also provides a historic outline of this theory. </p> <p>Interesting, Guillemin also shows here that pseudo-differential operators can be used to fine tune the theory of conormal distributions themselves -- giving a natural but unexpected application of pseudo-differential operators. </p> http://mathoverflow.net/questions/68680/counterexamples-in-pde/97250#97250 Answer by Uday for Counterexamples in PDE Uday 2012-05-17T18:49:45Z 2012-05-18T05:36:14Z <p>Lewy's example and most other allied examples of non-solvable operators have only complex coefficients. Leaving open the question of unsolvable operators with real coefficient. F.Treves in 1962 has constructed a fourth order operator iterating Lewy operator. </p> <p>If $P$ is Lewy operator then $PP\bar{P}\bar{P}$ is a real coefficient fourth order operator which is not local solvable. </p> http://mathoverflow.net/questions/96902/triangularizing-a-matrix-with-function-entries Triangularizing a matrix with function entries Uday 2012-05-14T14:22:34Z 2012-05-16T15:09:00Z <p>Hi Everybody!</p> <p>Given a matrix, with smooth functions as arguments is there any result which say about its triangularization?</p> <p>I know that, the question is in affirmative for diagonalizing a matrix which has distinct eigenvalues. Infact, we can show by Implicit function theorem that eigenvalues can be chosen to be $\mathcal{C}^{1}$functions. We can also calculate projection operators for the matrix using Cauchy integral formula. </p> <p>But, I have not found any result for triangularization. An answer or any references would be great help. Thank you. </p> <p>ADDED LATER: I have found in the Micheal Taylor's book 'Pseudo-differential operators' Page.72 a claim that for a matrix $K(\xi)$ there is always a measurable unitary matrix $U(\xi)$ such that $U^{-1}(\xi)K(\xi)U(\xi)$ is an upper triangular matrix. In this case $K(\xi)$ is smooth matrix in $\xi.$ He does not say exactly the name of this result though. </p> http://mathoverflow.net/questions/96800/combinatorial-interpretation-of-the-power-of-a-series/96827#96827 Answer by Uday for Combinatorial interpretation of the power of a series Uday 2012-05-13T10:30:06Z 2012-05-13T10:55:18Z <p>Nice question! You are looking for a combinatorial interpretation of nth-fold self-convolution of a sequence. A quick google serach gave me this <a href="http://www.emis.de/journals/INTEGERS/papers/l3/l3.pdf" rel="nofollow">result</a> on Catalan sequence. In this paper, a similar result is worked out on a series with Catalan coefficients. May be you can use similar idea for generic sequences. </p> http://mathoverflow.net/questions/95042/game-on-undirected-graphs Game on undirected graphs Uday 2012-04-24T16:38:23Z 2012-04-24T18:58:11Z <p>One of my friends suggested the following 2-player game. </p> <pre><code> Given an undirected graph(not necessarily connected), each player takes turns and removes either one vertex or two adjacent vertices. Removing a vertex from the graph consists of deleting the incident edges as well. The player who does not have any move loses. </code></pre> <p>Though the rules of the game look very simple, this turns out to be an interesting counting and connectivity game. Infact, using symmetry argument, we have also found that there is a winning strategy for the second player when the undirected graph is merely an even length cycle.</p> <p>The following are my questions:</p> <p>Does any graph theory concept suggest this game? Is there a standard game of this sort? Can we come up with a winning strategy for any player for the general graph? My guess is this game may be a version of game of Nim over graphs, I am not sure though. </p> <p>Thank you. </p> http://mathoverflow.net/questions/92696/excellent-uses-of-induction-and-recursion/92698#92698 Answer by Uday for Excellent uses of induction and recursion Uday 2012-03-30T17:01:48Z 2012-04-01T12:48:39Z <p>1)Proof of Euler's formula, V-E+F=2, with induction on F (number of faces). </p> <p>2)Backward induction proof of generalized AM-GM inequality. </p> <p>3)Proof of Heine-Borel theorem using <strike>Transfinite</strike> Topological induction.</p> http://mathoverflow.net/questions/91326/self-dual-normed-spaces-which-are-not-hilbert-spaces Self-dual normed spaces which are not Hilbert spaces Uday 2012-03-15T19:33:05Z 2012-03-17T18:54:32Z <p>Are there any examples of non-Hilbert normed spaces which are isomorphic (in the norm sense) to their dual spaces? Or, is there any result in Functional Analysis which says that if a space is self-dual it has to be Hilbert space. </p> <p>Since, we want isomorphism in the norm sense, examples like $\mathbb{R}^{n}$ are ruled out. The norms of the space and its dual have to be equal and not just equivalent. </p> <p>Thank you. </p> http://mathoverflow.net/questions/37933/what-is-the-implicit-function-theorem-good-for/88571#88571 Answer by Uday for What is the Implicit Function Theorem good for? Uday 2012-02-15T22:41:53Z 2012-03-16T15:57:31Z <p>One of the major applications of Implicit Function Theorem is the lesson it teaches:</p> <pre><code> Locally, Manifold Theory = Linear Algebra. </code></pre> <p>That is, locally, we can perform our calculus as if it is linear algebra. Solving simultaneous equations, discussing about linear independence of coordinates, basis set and mapping from one manifold to another can be viewed as linear transformations. Discuss the invertability of functions as if they are linear transformations. Infact by <a href="http://en.wikipedia.org/wiki/Darboux%27s_theorem" rel="nofollow">Darboux theorem</a>, in Symplectic manifold theory the linear algebra aspects is more prominent. </p> http://mathoverflow.net/questions/89556/easy-and-hard-problems-in-mathematics Easy and Hard problems in Mathematics Uday 2012-02-26T05:42:47Z 2012-03-15T08:26:07Z <p>Modified question:</p> <p>I would like to know some examples of problems in Mathematics, for pedagogical purposes, which do not involve difficult techiques to solve the problem but with a change of context turns them into monstrous-unimaginably difficult to solve problems. </p> <p>By changing the context I mean, by changing one class of objects in the problem to a related class of objects. For example, from directed graph to undirected graph or Zygmund class to Log-lipshitz class. By changing a 'less-than problem' to 'greater-than problem'. From 2-case problem to 3-case problem. There are plenty of such examples in Theoretical Computer Science or Computational Complexity theory. I need some examples in Mathematics. Lot of examples fall in this category but I am looking for only extreme examples like the ones I stated below. Since, this question is asked for pedagogical purpose it would be interesting if there is a story behind the problem.</p> <p>Examples of problems: </p> <ul> <li>Linear Programming to integer linear programming</li> <li>2-coloring to 3-coloring</li> <li>Eulerian graph to Hamiltonian graph</li> <li>Undirected graph case to directed graph case in Shannon's switching game</li> <li>2-SAT to 3-SAT</li> </ul> <p>One thought which motivated me to pose this question is: what if Konigsberg problem has been formulated as a vertex problem. Would Leonard Euler get inspried to create graph theory? No doubt, history speaks differently as Konigsberg problem is stated in terms of edges. Not only Euler solved this problem but created a branch of mathematics out of it! And I am not sure what turn of events would have taken place had the problem been posed in terms of vertices. </p> <p>IMHO, there are look-alike easy problems and hard problems coexisting but it is the easy problems which saved mathematicians day and hard ones which gave them incentive to work harder.</p> <p>Some pointers for hardness of problem: problems which need sophisticated tools, techniques which diverge from the routine ones, radical thinking or bold ideas to solve the them, like Poincare conjecture. Or, those problems which do not have adequate tools yet to attempt them, like (NP=P?). </p> <p>I would appreciate any answers in this direction. Thank you in advance. </p> http://mathoverflow.net/questions/90433/example-for-pairwise-triangularizable-but-not-all-three Example for pairwise triangularizable but not all three. Uday 2012-03-07T08:28:28Z 2012-03-07T16:27:54Z <p>I am not able give an example for the following problem on <a href="http://en.wikipedia.org/wiki/Triangular_matrix#Simultaneous_triangularisability" rel="nofollow">simultaneous triangularization</a>. So, I thought I will post it here. </p> <p>Give an example of three linear transformations $A,B$ and $C,$ such that the pairs $\lbrace A,B\rbrace$, $\lbrace B,C\rbrace$ and $\lbrace A,C\rbrace$ are simultaneously triangularizable, but the triplet $\lbrace A,B,C\rbrace$ is not simultaneously triangularizable. </p> <p>Thank you. </p> <p>ADDED LATER: For my need, I am looking for an example of linear transformations acting on vector spaces over $\mathbb{C}.$ </p> http://mathoverflow.net/questions/90129/orthogonality-in-non-inner-product-spaces Orthogonality in non-inner product spaces Uday 2012-03-03T17:47:13Z 2012-03-04T11:10:12Z <p>I have come across a notion of orthogonality of two vectors in a normed space not necessarily inner product space. Two vectors $x$ and $y$ in a normed space are said to be orthogonal (represented $x\perp y$) if $||x||\leq ||x+\alpha y||,$ for every $\alpha,$ a scalar. </p> <p>1) What is the rational behind the definition above? I guess, it has got something to do with minimum overlap between $x$ and $y$. </p> <p>2) Is this unique generalization of the concept of orthogonality from inner product spaces?</p> <p>Thank you. </p> http://mathoverflow.net/questions/88946/readings-for-an-honors-liberal-art-math-course/90057#90057 Answer by Uday for Readings for an honors liberal art math course Uday 2012-03-02T17:11:35Z 2012-03-03T09:38:40Z <p>Another good book though starts at an elementary level but covers lot of fundamental topics such as geometry, topology and calculus and could be highly recommended for the honors programs is: <a href="http://en.wikipedia.org/wiki/What_Is_Mathematics" rel="nofollow">What is Mathematics?</a> By Richard Courant and Herbert Robbins.</p> http://mathoverflow.net/questions/15028/do-you-find-your-students-are-less-competent-in-basic-algebra-and-arithmetic-and/89849#89849 Answer by Uday for Do you find your students are less competent in basic algebra and arithmetic, and, if so, do you believe that this is due to overuse of calculators at an early level? Uday 2012-02-29T09:19:03Z 2012-02-29T16:10:51Z <p>I feel both human-ability and technological-assitance should go hand-in-hand. We have to give equal importance to making students use a calculator and also learning how to do it by hand. I also feel we should encourage students to use softwares like Mathematica and Matlab. Otherwise, what advantage does a future mathematician have over old-timers! </p> <p>With this background, I feel there should be a clear emphasis on the interpretation of the results a student obtains on performing a calculation. </p> <pre><code> 'The purpose of computing is insight, not numbers.' -Hamming. </code></pre> <p>For example, we can use the series </p> <p>$\frac{1}{1+x} = 1-x+x^{2}+\cdots,$ for $|x|&lt;1$ to demonstrate the fact that if $|x|&lt;&lt;1$ (|x| is far far less than one) then $\frac{1}{1+x} \approx 1-x$ and show the results in a calculator.</p> <p>Say, $(1.001)^{-1}$ can be easily seen without the use of calculator as approximately equal $1-0.001=0.999.$ Division problem can be turned into a simple subtraction problem. After showing algebraic manipulation, we can show the calculator result and ask students to interpret the precision and give a good explanation. </p> <p>We could also enhance Mathlete competitions and make students learn to calculate mentally faster than a calculator, for which we need calculators! </p> http://mathoverflow.net/questions/88946/readings-for-an-honors-liberal-art-math-course/89160#89160 Answer by Uday for Readings for an honors liberal art math course Uday 2012-02-22T06:54:59Z 2012-02-22T16:46:42Z <p>The following books by American Mathematical Society are very good. </p> <p>1) Fixed points, by Yu.A.Shashkin</p> <p>2) Stories about Maxima and Minima, By V.M.Tikhomirov</p> <p>3) Intuitive Topology, By V.V.Prasolov </p> <p>These books translated from Russian are very insightful and are not voluminous. </p> <p>You can also look at the following combinatorial game theory book:</p> <p>Surreal Numbers: How Two Ex-Students Turned on to Pure Mathematics and Found Total Happiness. By Donald Knuth. </p> http://mathoverflow.net/questions/88946/readings-for-an-honors-liberal-art-math-course/88960#88960 Answer by Uday for Readings for an honors liberal art math course Uday 2012-02-19T20:16:32Z 2012-02-20T02:52:33Z <p>Few books to consider:</p> <p>1)<strong>Godel, Escher, Bach: An Eternal Golden Braid, By Douglas R Hofstadter</strong> : This Pulitzer prize winning book will be good for your needs. Has short and to great extent independent chapters and goes into the the meaning of mathematics, art, music and computing. Though the book looks voluminous it gives a possibility for selected reading. </p> <p>2)<strong>What is the name of this book?: The riddle of Dracula and other logical puzzles, By Raymond M Smullyan</strong> ("The most original, most profound, and most humorous collection of recreational logic and math problems ever written." — Martin Gardner.) </p> <p>3)<strong>Letter to young mathematician: the art of mentoring, By Ian Stewart</strong> : Subjects ranging from the philosophical to the practical--what mathematics is and why it's worth doing, the relationship between logic and proof, the role of beauty in mathematical thinking, the future of mathematics, how to deal with the peculiarities of the mathematical community are all discussed here. </p> <p>4)<strong>An Imaginary Tale: The Story of i [the square root of minus one], By Paul J. Nahin</strong> : Discusses imaginary numbers from a historical perspective. </p> <p>5) (added later)<strong>The Creative Process: Reflections on the Invention in the Arts and Sciences</strong> : Collection of essays written by some of the best minds like Poincare, Einstein, Mozart on how they got original ideas. Especially Poincare's essay is very insightful.</p> <p>6) (added later)<strong>I Want to Be a Mathematician. Springer-Verlag. By Paul Halmos</strong> : It is good to introduce students to Halmos writing. I am surprised nobody mentioned this. </p> http://mathoverflow.net/questions/88910/2-short-article-vs-a-long-one/88918#88918 Answer by Uday for 2 short article vs. a long one Uday 2012-02-19T09:43:01Z 2012-02-19T09:43:01Z <p>It depends! I am not giving any advice but I am only recalling an anti-measure theoretic quote in this context: </p> <pre><code> “The whole is greater than the sum of its parts.” - Aristotle </code></pre> <p>It may help to think in these lines. All the best!</p> http://mathoverflow.net/questions/88813/sobolev-embedding-proof-without-gagliardonirenbergsobolev-inequality-or-morrey Sobolev embedding proof without Gagliardo–Nirenberg–Sobolev inequality or Morrey's inequality Uday 2012-02-18T07:31:46Z 2012-02-18T16:25:56Z <p>Hello Everybody, </p> <p>Is there a proof of Sobolev embedding theorem without using the GNS or Morrey inequalities? If so, can you provide me with some references? </p> <p><strong>Background:</strong> I happened to attened a talk on Computational PDEs and Sobolev spaces. The speaker made a reference to a proof by S. L. Sobolev using polynomials. But, unfortunately he does not remember any references. </p> <p>Thank you in advance. </p> http://mathoverflow.net/questions/88540/how-to-motivate-and-present-epsilon-delta-proofs-to-undergraduates/88564#88564 Answer by Uday for How to motivate and present epsilon-delta proofs to undergraduates? Uday 2012-02-15T21:34:40Z 2012-02-16T01:04:34Z <p>Creating a $\epsilon-\delta$ game is really interesting. Thanks Charles Matthews! BTW, a similar strategy has been stated by Prof.Terry Tao in:Thinking and Explaining, <a href="http://mathoverflow.net/questions/38882" rel="nofollow">http://mathoverflow.net/questions/38882</a> (version: 2011-10-12)</p> <p>One other issue that usually undergrads feel elusive about in $\epsilon-\delta$ method is why is it "for every $\epsilon>0$ there exists a corresponding $\delta>0$" and <strong>not the other way round.</strong> In this context, the following simple analogy may illustrate the point: </p> <p>Assuming the discrete maths course is offered to CS students, I will consider software development analogy. In software development, there are essentially two parties. One Developer($\delta$ producer) and the other Client/User($\epsilon$ giver). </p> <p>We can ask the students which of the below models is preferred: </p> <p><strong>Model 1</strong>: Client gives a specification and developer abides by it. That is, client demands for certain feature in her product and developer accordingly makes the product. Analogously, fix $\epsilon>0$ in the range adjust $\delta$ in the domain.</p> <p><strong>Model 2</strong>: Developer gives certain product and client should accept it however pathetic it may be. Analogously, fix $\delta>0$ and expect $\epsilon>0$ to be satisfied.</p> <p>Model 1 is naturally preferred. And that is our $\epsilon-\delta$ method.</p> <p>Of course, we can change the setting depending on the target students(engineers/physicists/biologists etc. ). </p> http://mathoverflow.net/questions/87937/functions-of-pseudodifferential-operators/88545#88545 Answer by Uday for Functions of Pseudodifferential Operators Uday 2012-02-15T19:36:22Z 2012-02-15T19:47:08Z <p>Since the question posed is about the "In what way does the type of operator or the type of function matter?", I thought the following observation will be apt:</p> <p>As pointed out by Liviu Nicolaescu in the comment above, Taylor's approach seems to have much wider applicability when it comes to functional calculus. In fact in page 295 of Taylor's book it is mentioned that Seeley's results form a special case of the result. </p> <p>Moreover, these methods have gone beyond elliptic operators. For instance, <a href="http://onlinelibrary.wiley.com/doi/10.1002/cpa.3160320403/abstract" rel="nofollow">Uhlmann, Melrose</a> and <a href="http://projecteuclid.org/DPubS?service=UI&amp;version=1.0&amp;verb=Display&amp;handle=euclid.dmj/1077314493" rel="nofollow">Guillemin</a> have developed a framework of distributions whose wavefront sets are in several Lagrangian intersecting manifolds (pseudodifferential operators with singular symbols) for a functional calculus on <strong>real principal-type operators, operators of double characteristics, wave operators</strong>. Principal symbols also have been computed for these operators and all the computations are purely symbolic. </p> http://mathoverflow.net/questions/117437/the-distribution-of-roots-of-elliptic-polynomial Comment by Uday Uday 2012-12-28T19:16:08Z 2012-12-28T19:16:08Z I think G.B.Folland discusses this in his Introductory book on PDE. http://mathoverflow.net/questions/117263/optimization-version-of-the-sylvester-equation/117319#117319 Comment by Uday Uday 2012-12-27T16:35:13Z 2012-12-27T16:35:13Z @Suvrit Thank you for the answer. Your answer settles the fact that there exists a solution. But, my original interest, which I unfortunately did not make it clear in my post, is to get some quantitative information on the bounds of the solution w.r.t the eigenvalues of $A$ and $B$. http://mathoverflow.net/questions/116150/triangularizing-a-function-matrix-with-smooth-eigenvlaues/116151#116151 Comment by Uday Uday 2012-12-27T15:37:10Z 2012-12-27T15:37:10Z I have figured out a way to translate the paper. Thank you once again. http://mathoverflow.net/questions/117263/optimization-version-of-the-sylvester-equation Comment by Uday Uday 2012-12-27T05:52:47Z 2012-12-27T05:52:47Z @Igor Khavkine Yes, my interest is in the case when the matrices have overlapping spectra. I have edited the question to reflect this. http://mathoverflow.net/questions/117263/optimization-version-of-the-sylvester-equation/117265#117265 Comment by Uday Uday 2012-12-27T05:41:39Z 2012-12-27T05:41:39Z Thank you for the reference. http://mathoverflow.net/questions/116150/triangularizing-a-function-matrix-with-smooth-eigenvlaues/116151#116151 Comment by Uday Uday 2012-12-12T09:33:00Z 2012-12-12T09:33:00Z @Andr&#225;s B&#225;tkai Thank you for the reference. I will try to get this paper. Is there an English translation of this paper? http://mathoverflow.net/questions/116150/triangularizing-a-function-matrix-with-smooth-eigenvlaues Comment by Uday Uday 2012-12-12T09:30:22Z 2012-12-12T09:30:22Z @Denis Serre Yes. Kato's book discusses Jordan form. But, I find that questions about Jordan form and triangular form are a bit different. For example, the matrix $$\left(\begin{array}{cc} 1&amp;z\\ 0&amp;1 \end{array}\right)$$ is trivially triangulariable with smooth entries but cannot be written in Jordan form at $z=0$. http://mathoverflow.net/questions/106234/simple-functions-in-the-product-space Comment by Uday Uday 2012-09-03T11:51:44Z 2012-09-03T11:51:44Z Real Analysis: Modern techniques and their applications by G.B.Folland is a good reference. http://mathoverflow.net/questions/105824/what-is-the-non-intuitive-part-in-sphere-eversion-turning-inside-out/105830#105830 Comment by Uday Uday 2012-08-30T07:13:35Z 2012-08-30T07:13:35Z @Mark Thank you. The inputs are sufficient for further exploration. http://mathoverflow.net/questions/105021/why-take-complex-powers-of-pseudo-differential-operators/105027#105027 Comment by Uday Uday 2012-08-21T05:27:06Z 2012-08-21T05:27:06Z Thanks, Rafe. So, 'Spectral theory of pseudo-differential operators' is the answer to my question. http://mathoverflow.net/questions/100905/duality-argument-in-pde/100908#100908 Comment by Uday Uday 2012-06-29T15:18:04Z 2012-06-29T15:18:04Z Are you referring to Holmgren's uniqueness theorem? http://mathoverflow.net/questions/100933/continuous-singular-support Comment by Uday Uday 2012-06-29T15:06:51Z 2012-06-29T15:06:51Z Does singular support in the title refer to points of discontinuity of the function? And, does $F_{\sigma}$ refer to a set which is countable union of closed sets? http://mathoverflow.net/questions/98050/the-game-of-removing-two-vertices-in-a-graph Comment by Uday Uday 2012-05-26T20:51:32Z 2012-05-26T20:51:32Z I had asked a similar question in: <a href="http://mathoverflow.net/questions/95042/game-on-undirected-graphs" rel="nofollow" title="game on undirected graphs">mathoverflow.net/questions/95042/&hellip;</a>. Some of the answers therein may help. http://mathoverflow.net/questions/97296/second-order-operator-with-real-coefficients-and-not-locally-solvable/97347#97347 Comment by Uday Uday 2012-05-21T03:51:23Z 2012-05-21T03:51:23Z Nice example. Thanks! http://mathoverflow.net/questions/96902/triangularizing-a-matrix-with-function-entries/96904#96904 Comment by Uday Uday 2012-05-14T18:05:39Z 2012-05-14T18:05:39Z I will check this. Thanks a million!