Let $m_i\in \mathbb{N}, 1\leq i \leq n $ such that wlog if $m_i < m_j\in \mathbb{Z^+}$ then $i < j$. Consider the Vandermonde matrix $$V= \begin{bmatrix} 1 & 1 & 1 & \ldots & 1 \\ x_1^{m_1} & x_2^{m_1} & x_3^{m_1} & \ldots & x_{n+1}^{m_1} \\ x_1^{m_2} & x_2^{m_2} & x_3^{m_2} & \ldots & x_{n+1}^{m_2} \\ \vdots & \vdots & \vdots & \ddots & \vdots \\ x_1^{m_n} & x_2^{m_n} & x_3^{m_n} & \ldots & x_{n+1}^{m_n} \\ \end{bmatrix}$$ Under Whatwhat conditions is the generalized Vandermonde Matrix Invertiblematrix invertible? It is clear that if one lets $x_i=x_j$,then the determinant is Zerozero, and therefore the principle Vandermonde Determinant $V_p=\prod_{1 \leq i < j\leq n}^n(x_i-x_j)$ can be factored from the $det(V)$$\det(V)$. What remains is the schur function, which is a homogeneous polynomial of degree d which depends on $n$, which symmetric over its variables $x_i,1\leq i\leq n$. There is a proof of the fact that the coefficients of the schur function are positive integers which was given by Mitchel long ago.
For $n=3$ things become difficult already as $$V_3= \begin{bmatrix} 1 & 1 & 1\\ x_1^{m_1} & x_2^{m_1} & x_3^{m_1}\\ x_1^{m_2} & x_2^{m_2} & x_3^{m_2} \end{bmatrix}$$ $det(V_3) = x_2^{m_2} x_1^{m_1}-x_3^{m_2} x_1^{m_1}-x_2^{m_1} x_1^{m_2}+x_3^{m_1} x_1^{m_2}-x_2^{m_2} x_3^{m_1}+x_2^{m_1} x_3^{m_2}$$\det(V_3) = x_2^{m_2} x_1^{m_1}-x_3^{m_2} x_1^{m_1}-x_2^{m_1} x_1^{m_2}+x_3^{m_1} x_1^{m_2}-x_2^{m_2} x_3^{m_1}+x_2^{m_1} x_3^{m_2}$.
What are the conditions under which the generalized Vandermonde matrix is invertible over $\mathbb{R^n}$ or $\mathbb{C^n}$? Is there Hopehope?
Well yeahyes, a little bit.There There are some results one could see from Mitchel's result about the positivity of the coefficients of the Schur function. If we are working over $\mathbb{R^n}$, then as a consequence of the positivity of the coefficients mentioned by Mitchel, one can deduce that if $x_i$ are distinct and positive for $1 \leq i \leq n$, then the schurSchur function takes on positive values and therefore non-zero. This result is mentioned in this Paperpaper.
1)Let $V_3$ be a the following $3$x$3$ matrix: $$V_3= \begin{bmatrix} 1 & 1 & 1\\ x_1 & x_2 & x_3\\ x_1^{3} & x_2^{3} & x_3^{3} \end{bmatrix}$$ where $m_1 = 1, m_2 = 3$, then $det(V)=-(x_1-x_2) (x_1-x_3) (x_2-x_3) (x_1+x_2+x_3)$$\det(V)=-(x_1-x_2) (x_1-x_3) (x_2-x_3) (x_1+x_2+x_3)$, so our schurSchur function is the elementary symmetric function $x_1+x_2+x_3$ which is non-zero if $x_j \neq x_i \in \mathbb{R^+}$ $\forall i,j$
$det(V)=-x_2^4 x_1^6+x_3^4 x_1^6+x_2^6 x_1^4-x_3^6 x_1^4+x_2^4 x_3^6-x_2^6 x_3^4$$\det(V)=-x_2^4 x_1^6+x_3^4 x_1^6+x_2^6 x_1^4-x_3^6 x_1^4+x_2^4 x_3^6-x_2^6 x_3^4$
$det(V)=-(x_1-x_2) (x_1+x_2) (x_1-x_3) (x_2-x_3) (x_1+x_3) (x_2+x_3) (x_1^2 x_2^2+x_3^2 x_2^2+x_1^2 x_3^2)$$\det(V)=-(x_1-x_2) (x_1+x_2) (x_1-x_3) (x_2-x_3) (x_1+x_3) (x_2+x_3) (x_1^2 x_2^2+x_3^2 x_2^2+x_1^2 x_3^2)$, so our schurSchur function is $ (x_1+x_2)(x_1+x_3) (x_2+x_3) (x_1^2 x_2^2+x_3^2 x_2^2+x_1^2 x_3^2)$ which is non-zero if $x_j \neq x_i \in \mathbb{R^+}$ $\forall i,j$
$det(V)=-(x_1-x_2) (x_1-x_3) (x_2-x_3)$$\det(V)=-(x_1-x_2) (x_1-x_3) (x_2-x_3)$ *
So our schurSchur function is everything that we have after dividing out by $V_p$. This function is non-zero if $x_j \neq x_i \in \mathbb{R^+}$ $\forall i,j$
My goal is to really answer the following interesting question, Let ${m_i}$, $i \in \mathbb{N}$ be an increasing sequence of distinct positive integers, then consider the schurSchur function obtained by dividing out the following Vandermonde Determinantdeterminant by the principle Vandermonde:
where $m_{i_j}$ are terms in the sequence ${m_i}$, $i \in \mathbb{N}$ such that $m_{i_{j_1}}< m_{i_{j_2}}$ implies $j_1 < j_2$. Let $\Gamma$ ={all possible $m_{i_j}, 1 \leq j \leq n $}, then each element of $\Gamma$ corresponds to a unique schurSchur function. Let $S_{\Gamma}$ ={schurSchur functions induced by $\Gamma$}. Now Let $s \in S_{\Gamma}$ and $Z_s$ ={zeros of $s$}, then I would like to show that $\cap_{s \in S_{\Gamma} }Z_s$ is empty, provided that there are no non-trivial relations between the variables of the schurSchur function, i.e. the $n$ variables of the schurSchur function form a free abelian group of rank $n$, i.e. if the product of the coordinates of a zero of the schurSchur function does not satisfy that condition then you should exclude it.
As pointed out by Emmanuel Briand in the comments, if the sequence $m_i$ contains $n$ consecutive integers, then the zeros of the corresponding schurSchur function are trivial as they are of the form $(0,\cdots , 1, \cdots , 0)$ where 1 is located in the $i^{th}$ position. As a special case, you can see that if $m_i$ contains $1,2,\cdots , n-1$, then the answer to the question above is positive, i.e. the $\cap_{s \in S_{\Gamma} }Z_s$ is empty.