grandes-ecoles

Papers (176)
2025
centrale-maths1__official 40 centrale-maths2__official 36 mines-ponts-maths1__mp 17 mines-ponts-maths1__pc 21 mines-ponts-maths1__psi 21 mines-ponts-maths2__mp 28 mines-ponts-maths2__pc 23 mines-ponts-maths2__psi 25 polytechnique-maths-a__mp 35 polytechnique-maths__fui 9 polytechnique-maths__pc 27 x-ens-maths-a__fui 10 x-ens-maths-a__mp 18 x-ens-maths-b__mp 6 x-ens-maths-c__mp 6 x-ens-maths-d__mp 31 x-ens-maths__pc 27 x-ens-maths__psi 30
2024
centrale-maths1__official 21 centrale-maths2__official 28 geipi-polytech__maths 9 mines-ponts-maths1__mp 23 mines-ponts-maths1__psi 9 mines-ponts-maths2__mp 14 mines-ponts-maths2__pc 19 mines-ponts-maths2__psi 20 polytechnique-maths-a__mp 42 polytechnique-maths-b__mp 27 x-ens-maths-a__mp 43 x-ens-maths-b__mp 29 x-ens-maths-c__mp 22 x-ens-maths-d__mp 41 x-ens-maths__pc 20 x-ens-maths__psi 23
2023
centrale-maths1__official 37 centrale-maths2__official 32 e3a-polytech-maths__mp 4 mines-ponts-maths1__mp 14 mines-ponts-maths1__pc 21 mines-ponts-maths1__psi 21 mines-ponts-maths2__mp 21 mines-ponts-maths2__pc 13 mines-ponts-maths2__psi 22 polytechnique-maths__fui 3 x-ens-maths-a__mp 24 x-ens-maths-b__mp 10 x-ens-maths-c__mp 10 x-ens-maths-d__mp 10 x-ens-maths__pc 22
2022
centrale-maths1__mp 22 centrale-maths1__pc 33 centrale-maths1__psi 42 centrale-maths2__mp 26 centrale-maths2__pc 37 centrale-maths2__psi 40 mines-ponts-maths1__mp 26 mines-ponts-maths1__pc 20 mines-ponts-maths1__psi 23 mines-ponts-maths2__mp 22 mines-ponts-maths2__pc 9 mines-ponts-maths2__psi 18 x-ens-maths-a__mp 8 x-ens-maths-b__mp 19 x-ens-maths-c__mp 17 x-ens-maths-d__mp 47 x-ens-maths1__mp 13 x-ens-maths2__mp 26 x-ens-maths__pc 7 x-ens-maths__pc_cpge 14 x-ens-maths__psi 22 x-ens-maths__psi_cpge 26
2021
centrale-maths1__mp 34 centrale-maths1__pc 36 centrale-maths1__psi 28 centrale-maths2__mp 21 centrale-maths2__pc 38 centrale-maths2__psi 28 x-ens-maths2__mp 35 x-ens-maths__pc 29
2020
centrale-maths1__mp 42 centrale-maths1__pc 36 centrale-maths1__psi 38 centrale-maths2__mp 2 centrale-maths2__pc 35 centrale-maths2__psi 39 mines-ponts-maths1__mp_cpge 22 mines-ponts-maths2__mp_cpge 19 x-ens-maths-a__mp_cpge 10 x-ens-maths-b__mp_cpge 19 x-ens-maths-c__mp 10 x-ens-maths-d__mp 13 x-ens-maths1__mp 13 x-ens-maths2__mp 20 x-ens-maths__pc 6
2019
centrale-maths1__mp 37 centrale-maths1__pc 40 centrale-maths1__psi 38 centrale-maths2__mp 37 centrale-maths2__pc 39 centrale-maths2__psi 46 x-ens-maths1__mp 24 x-ens-maths__pc 18 x-ens-maths__psi 9
2018
centrale-maths1__mp 21 centrale-maths1__pc 31 centrale-maths1__psi 39 centrale-maths2__mp 23 centrale-maths2__pc 35 centrale-maths2__psi 30 x-ens-maths1__mp 18 x-ens-maths2__mp 13 x-ens-maths__pc 17 x-ens-maths__psi 20
2017
centrale-maths1__mp 45 centrale-maths1__pc 22 centrale-maths1__psi 17 centrale-maths2__mp 30 centrale-maths2__pc 28 centrale-maths2__psi 44 x-ens-maths1__mp 24 x-ens-maths2__mp 7 x-ens-maths__pc 17 x-ens-maths__psi 19
2016
centrale-maths1__mp 41 centrale-maths1__pc 31 centrale-maths1__psi 33 centrale-maths2__mp 25 centrale-maths2__pc 42 centrale-maths2__psi 17 x-ens-maths1__mp 10 x-ens-maths2__mp 32 x-ens-maths__pc 1 x-ens-maths__psi 20
2015
centrale-maths1__mp 18 centrale-maths1__pc 11 centrale-maths1__psi 42 centrale-maths2__mp 44 centrale-maths2__pc 1 centrale-maths2__psi 14 x-ens-maths1__mp 16 x-ens-maths2__mp 19 x-ens-maths__pc 30 x-ens-maths__psi 20
2014
centrale-maths1__mp 28 centrale-maths1__pc 26 centrale-maths1__psi 36 centrale-maths2__mp 24 centrale-maths2__pc 23 centrale-maths2__psi 29 x-ens-maths2__mp 13
2013
centrale-maths1__mp 3 centrale-maths1__pc 45 centrale-maths1__psi 20 centrale-maths2__mp 32 centrale-maths2__pc 50 centrale-maths2__psi 32 x-ens-maths1__mp 14 x-ens-maths2__mp 10 x-ens-maths__pc 22 x-ens-maths__psi 9
2012
centrale-maths1__pc 23 centrale-maths1__psi 20 centrale-maths2__mp 27 centrale-maths2__psi 20
2011
centrale-maths1__mp 27 centrale-maths1__pc 15 centrale-maths1__psi 21 centrale-maths2__mp 29 centrale-maths2__pc 8 centrale-maths2__psi 28
2010
centrale-maths1__mp 7 centrale-maths1__pc 23 centrale-maths1__psi 9 centrale-maths2__mp 10 centrale-maths2__pc 36 centrale-maths2__psi 27
2018 centrale-maths1__psi

39 maths questions

Q1 Matrices Structured Matrix Characterization View
Show that $\operatorname{Toep}_{n}(\mathbb{C})$ is a vector subspace of $\mathcal{M}_{n}(\mathbb{C})$. Give a basis for it and specify its dimension.
Q2 Matrices Matrix Algebra and Product Properties View
Show that if two matrices $A$ and $B$ commute $(AB = BA)$ and if $P$ and $Q$ are two polynomials of $\mathbb{C}[X]$, then $P(A)$ and $Q(B)$ commute.
Q3 Matrices Eigenvalue and Characteristic Polynomial Analysis View
Let $A = \left(\begin{array}{cc} a & b \\ c & a \end{array}\right)$ be a Toeplitz matrix of size $2 \times 2$, where $(a, b, c)$ are complex numbers. Give the characteristic polynomial of $A$.
Q4 Matrices Diagonalizability and Similarity View
Let $A = \left(\begin{array}{cc} a & b \\ c & a \end{array}\right)$ be a Toeplitz matrix of size $2 \times 2$, where $(a, b, c)$ are complex numbers. Discuss, depending on the values of $(a, b, c)$, the diagonalizability of $A$.
Q5 Matrices Diagonalizability and Similarity View
Let $M = \left(\begin{array}{ll} a & b \\ c & d \end{array}\right)$ be a matrix of $\mathcal{M}_{2}(\mathbb{C})$. Show that $M$ is similar to a matrix of type $\left(\begin{array}{cc} \alpha & 0 \\ 0 & \beta \end{array}\right)$ or of type $\left(\begin{array}{cc} \alpha & \gamma \\ 0 & \alpha \end{array}\right)$, where $\alpha, \beta$ and $\gamma$ are complex numbers with $\alpha \neq \beta$.
Q6 Matrices Diagonalizability and Similarity View
Deduce that every matrix of $\mathcal{M}_{2}(\mathbb{C})$ is similar to a Toeplitz matrix.
Q7 Matrices Second-order linear recurrence relation View
A tridiagonal matrix is a Toeplitz matrix of the form $T(0,\ldots,0,t_{-1},t_0,t_1,0,\ldots,0)$, i.e. a matrix of the form $$A_n(a,b,c) = \left(\begin{array}{cccc} a & b & & (0) \\ c & a & \ddots & \\ & \ddots & \ddots & b \\ (0) & & c & a \end{array}\right)$$ where $(a,b,c)$ are complex numbers. We fix $(a,b,c)$ three complex numbers such that $bc \neq 0$. Let $\lambda \in \mathbb{C}$ be an eigenvalue of $A_n(a,b,c)$ and $X = \left(\begin{array}{c} x_1 \\ \vdots \\ x_n \end{array}\right) \in \mathbb{C}^n$ be an associated eigenvector.
Show that if we set $x_0 = 0$ and $x_{n+1} = 0$, then $(x_1, \ldots, x_n)$ are the terms of rank varying from 1 to $n$ of a sequence $(x_k)_{k \in \mathbb{N}}$ satisfying $x_0 = 0, x_{n+1} = 0$ and $$\forall k \in \mathbb{N}, \quad bx_{k+2} + (a-\lambda)x_{k+1} + cx_k = 0$$
Q8 Sequences and series, recurrence and convergence Second-order linear recurrence relation View
Recall the expression of the general term of the sequence $(x_k)_{k \in \mathbb{N}}$ as a function of the solutions of the equation $$bx^2 + (a-\lambda)x + c = 0 \tag{I.1}$$
Q9 Sequences and series, recurrence and convergence Second-order linear recurrence relation View
Using the conditions imposed on $x_0$ and $x_{n+1}$, show that (I.1) admits two distinct solutions $r_1$ and $r_2$.
Q10 Invariant lines and eigenvalues and vectors Roots of Unity and Cyclotomic Properties View
Show that $r_1$ and $r_2$ are nonzero and that $r_1/r_2$ belongs to $\mathbb{U}_{n+1}$.
Q11 Invariant lines and eigenvalues and vectors Roots of Unity and Cyclotomic Properties View
Using the equation (I.1) satisfied by $r_1$ and $r_2$, determine $r_1 r_2$ and $r_1 + r_2$. Deduce that there exists an integer $\ell \in \llbracket 1, n \rrbracket$ and a complex number $\rho$ satisfying $\rho^2 = bc$ such that $$\lambda = a + 2\rho \cos\left(\frac{\ell \pi}{n+1}\right)$$
Q12 Invariant lines and eigenvalues and vectors Roots of Unity and Cyclotomic Properties View
Deduce that there exists $\alpha \in \mathbb{C}$ such that, for all $k$ in $\llbracket 0, n+1 \rrbracket$, $x_k = 2\mathrm{i}\alpha \frac{\rho^k}{b^k} \sin\left(\frac{\ell k \pi}{n+1}\right)$.
Q13 Invariant lines and eigenvalues and vectors Diagonalize a matrix explicitly View
Conclude that $A_n(a,b,c)$ is diagonalizable and give its eigenvalues.
Q14 Invariant lines and eigenvalues and vectors Matrix Power Computation and Application View
We set $M_n = \left(\begin{array}{ccccc} 0 & 1 & 0 & \cdots & 0 \\ 0 & 0 & \ddots & \ddots & \vdots \\ \vdots & & \ddots & \ddots & 0 \\ 0 & & & \ddots & 1 \\ 1 & 0 & \cdots & \cdots & 0 \end{array}\right)$ and $\omega_n = \mathrm{e}^{2i\pi/n}$.
Calculate $M_n^2, \ldots, M_n^n$. Show that $M_n$ is invertible and give an annihilating polynomial of $M_n$.
Q15 Invariant lines and eigenvalues and vectors Diagonalize a matrix explicitly View
We set $M_n = \left(\begin{array}{ccccc} 0 & 1 & 0 & \cdots & 0 \\ 0 & 0 & \ddots & \ddots & \vdots \\ \vdots & & \ddots & \ddots & 0 \\ 0 & & & \ddots & 1 \\ 1 & 0 & \cdots & \cdots & 0 \end{array}\right)$ and $\omega_n = \mathrm{e}^{2i\pi/n}$.
Justify that $M_n$ is diagonalizable. Specify its eigenvalues (expressed using $\omega_n$) and give a basis of eigenvectors of $M_n$.
Q16 Invariant lines and eigenvalues and vectors Diagonalizability and Similarity View
We set $M_n = \left(\begin{array}{ccccc} 0 & 1 & 0 & \cdots & 0 \\ 0 & 0 & \ddots & \ddots & \vdots \\ \vdots & & \ddots & \ddots & 0 \\ 0 & & & \ddots & 1 \\ 1 & 0 & \cdots & \cdots & 0 \end{array}\right)$ and $\omega_n = \mathrm{e}^{2i\pi/n}$.
We set $\Phi_n = \left(\omega_n^{(p-1)(q-1)}\right)_{1 \leqslant p,q \leqslant n} \in \mathcal{M}_n(\mathbb{C})$. Justify that $\Phi_n$ is invertible and give without calculation the value of the matrix $\Phi_n^{-1} M_n \Phi_n$.
Q18 Invariant lines and eigenvalues and vectors Structured Matrix Characterization View
Conversely, if $P \in \mathbb{C}[X]$, show, using a Euclidean division of $P$ by a suitably chosen polynomial, that $P(M_n)$ is a circulant matrix.
Q19 Invariant lines and eigenvalues and vectors Structured Matrix Characterization View
Show that the set of circulant matrices is a vector subspace of $\operatorname{Toep}_n(\mathbb{C})$, stable under multiplication and transposition.
Q20 Invariant lines and eigenvalues and vectors Spectral properties of structured or special matrices View
Show that every circulant matrix is diagonalizable. Specify its eigenvalues and a basis of eigenvectors.
Q21 Invariant lines and eigenvalues and vectors Linear Transformation and Endomorphism Properties View
Show that if $M$ is in $\mathcal{M}_n(\mathbb{C})$, then the following propositions are equivalent:
i. there exists $x_0$ in $\mathbb{C}^n$ such that $(x_0, f_M(x_0), \ldots, f_M^{n-1}(x_0))$ is a basis of $\mathbb{C}^n$;
ii. $M$ is similar to the matrix $C(a_0, \ldots, a_{n-1})$ defined by $$C(a_0, \ldots, a_{n-1}) = \left(\begin{array}{ccccc} 0 & 0 & \cdots & 0 & a_0 \\ 1 & \ddots & & \vdots & a_1 \\ 0 & \ddots & \ddots & \vdots & \vdots \\ \vdots & \ddots & \ddots & 0 & \vdots \\ 0 & \cdots & 0 & 1 & a_{n-1} \end{array}\right)$$ where $(a_0, \ldots, a_{n-1})$ are complex numbers.
Q22 Invariant lines and eigenvalues and vectors Diagonalizability determination or proof View
Let $M$ be in $\mathcal{M}_n(\mathbb{C})$. We assume that $f_M$ is diagonalizable. We denote by $(\lambda_1, \ldots, \lambda_n)$ its eigenvalues (not necessarily distinct) and by $(e_1, \ldots, e_n)$ a basis of eigenvectors associated with these eigenvalues. Let $u = \sum_{i=1}^{n} u_i e_i$ be a vector of $\mathbb{C}^n$ where $(u_1, \ldots, u_n)$ are $n$ complex numbers.
Give a necessary and sufficient condition on $(u_1, \ldots, u_n, \lambda_1, \ldots, \lambda_n)$ for $(u, f_M(u), \ldots, f_M^{n-1}(u))$ to be a basis of $\mathbb{C}^n$.
Q23 Invariant lines and eigenvalues and vectors Diagonalizability determination or proof View
Deduce a necessary and sufficient condition for a diagonalizable endomorphism to be cyclic. Then characterize its cyclic vectors.
Q24 Roots of polynomials Eigenvalue-root connection for matrices or linear operators View
Let $(a_0, \ldots, a_{n-1}) \in \mathbb{C}^n$. Let $\lambda$ be a complex number. By discussing in $\mathbb{C}^n$ the system $C(a_0, \ldots, a_{n-1})X = \lambda X$, show that $\lambda$ is an eigenvalue of $C(a_0, \ldots, a_{n-1})$ if and only if $\lambda$ is a root of a polynomial of $\mathbb{C}[X]$ to be specified.
Q25 Roots of polynomials Eigenvalue and Characteristic Polynomial Analysis View
Let $(a_0, \ldots, a_{n-1}) \in \mathbb{C}^n$. If $\lambda$ is a root of the polynomial identified in Q24, determine the eigenspace of $C(a_0, \ldots, a_{n-1})$ associated with the eigenvalue $\lambda$ and specify its dimension.
Q26 Invariant lines and eigenvalues and vectors Diagonalizability and Similarity View
Deduce a necessary and sufficient condition for a cyclic matrix to be diagonalizable.
Q27 Invariant lines and eigenvalues and vectors Linear Transformation and Endomorphism Properties View
Let $M$ be a cyclic matrix and $x_0$ be a cyclic vector of $f_M$. Let $P \in \mathbb{C}[X]$. Show that $P(f_M) \in \mathcal{C}(f_M)$, where $\mathcal{C}(f_M) = \{g \in \mathcal{L}(\mathbb{C}^n) \mid f_M \circ g = g \circ f_M\}$.
Q28 Invariant lines and eigenvalues and vectors Linear Transformation and Endomorphism Properties View
Let $M$ be a cyclic matrix and $x_0$ be a cyclic vector of $f_M$. Let $g \in \mathcal{C}(f_M)$. Show that there exist $(\alpha_0, \ldots, \alpha_{n-1}) \in \mathbb{C}^n$ such that $g = \alpha_0 Id_{\mathbb{C}^n} + \alpha_1 f_M + \cdots + \alpha_{n-1} f_M^{n-1}$. One may use the basis $(x_0, f_M(x_0), \ldots, f_M^{n-1}(x_0))$ and express $g(x_0)$ in this basis.
Q29 Invariant lines and eigenvalues and vectors Linear Transformation and Endomorphism Properties View
Let $M$ be a cyclic matrix and $x_0$ be a cyclic vector of $f_M$. The set $\mathcal{C}(f_M) = \{g \in \mathcal{L}(\mathbb{C}^n) \mid f_M \circ g = g \circ f_M\}$ is sought to be shown to be the set of polynomials in $f_M$. Conclude.
Q30 Roots of polynomials Diagonalizability determination or proof View
Let $N = \left(\begin{array}{ccccc} 0 & 0 & \cdots & \cdots & 0 \\ 1 & 0 & & & \vdots \\ 0 & \ddots & \ddots & & \vdots \\ \vdots & \ddots & \ddots & \ddots & \vdots \\ 0 & \cdots & 0 & 1 & 0 \end{array}\right)$.
Give the eigenvalues of $N$ and the associated eigenspaces. Is it diagonalizable?
Q31 Matrices Linear Transformation and Endomorphism Properties View
Let $N = \left(\begin{array}{ccccc} 0 & 0 & \cdots & \cdots & 0 \\ 1 & 0 & & & \vdots \\ 0 & \ddots & \ddots & & \vdots \\ \vdots & \ddots & \ddots & \ddots & \vdots \\ 0 & \cdots & 0 & 1 & 0 \end{array}\right)$.
Is the matrix $N$ cyclic?
Q32 Matrices Structured Matrix Characterization View
Let $N = \left(\begin{array}{ccccc} 0 & 0 & \cdots & \cdots & 0 \\ 1 & 0 & & & \vdots \\ 0 & \ddots & \ddots & & \vdots \\ \vdots & \ddots & \ddots & \ddots & \vdots \\ 0 & \cdots & 0 & 1 & 0 \end{array}\right)$.
Show that the set of matrices that commute with $N$ is the set of lower triangular Toeplitz matrices.
Q33 Matrices Matrix Algebra and Product Properties View
Show that if $i$ and $j$ are in $\llbracket -n+1, n-1 \rrbracket$, if $A \in \Delta_i$ and $B \in \Delta_j$, then $AB \in \Delta_{i+j}$.
Q34 Matrices Matrix Algebra and Product Properties View
Deduce that if $A \in H_i$ and $B \in H_j$, then $AB \in H_{i+j}$.
Q35 Matrices Linear System and Inverse Existence View
Let $C$ be a nilpotent matrix. Show that $I_n + C$ is invertible and that $$\left(I_n + C\right)^{-1} = I_n - C + C^2 + \cdots + (-1)^{n-1} C^{n-1}$$
Q36 Matrices Proof That a Map Has a Specific Property View
We assume that $k \geqslant 0$ and that $C$ is a matrix in $\Delta_{k+1}$. We set $P = I_n + C$. Show that $P$ is invertible and that $P^{-1} \in \bigoplus_{p=0}^{n-1} \Delta_{p(k+1)}$.
Q37 Matrices Direct Proof of a Stated Identity or Equality View
We assume that $k \geqslant 0$ and that $C$ is a matrix in $\Delta_{k+1}$. We set $P = I_n + C$. We consider the endomorphism $\varphi$ of $\mathcal{M}_n(\mathbb{R})$ defined by $\forall M \in \mathcal{M}_n(\mathbb{R}), \varphi: M \mapsto P^{-1}MP$.
Let $i \in \llbracket 0, k \rrbracket$ and $M \in \Delta_i$. Show that there exists $M'$ in $H_{k+1}$ such that $\varphi(M) = M + M'$.
Q38 Matrices Direct Proof of a Stated Identity or Equality View
We assume that $k \geqslant 0$ and that $C$ is a matrix in $\Delta_{k+1}$. We set $P = I_n + C$. We consider the endomorphism $\varphi$ of $\mathcal{M}_n(\mathbb{R})$ defined by $\forall M \in \mathcal{M}_n(\mathbb{R}), \varphi: M \mapsto P^{-1}MP$. The matrix $N$ being the matrix defined in III.A.4, show that there exists $N'$ in $H_{k+1}$ such that $$\varphi(N) = N + NC - CN + N'$$
Q39 Matrices Direct Proof of a Stated Identity or Equality View
We assume that $k \geqslant 0$ and that $C$ is a matrix in $\Delta_{k+1}$. We set $P = I_n + C$. We consider the endomorphism $\varphi$ of $\mathcal{M}_n(\mathbb{R})$ defined by $\forall M \in \mathcal{M}_n(\mathbb{R}), \varphi: M \mapsto P^{-1}MP$. Let $T$ be an upper triangular matrix. We set $A = N + T$, $B = \varphi(A)$. Show that $B \in H_{-1}$ and that $$\begin{cases} \forall i \in \llbracket -1, k-1 \rrbracket, \quad B^{(i)} = A^{(i)} \\ B^{(k)} = A^{(k)} + NC - CN \end{cases}$$
Q40 Matrices Linear Transformation and Endomorphism Properties View
We define the operators $$\mathcal{S}: \begin{cases} \mathcal{M}_n(\mathbb{R}) \rightarrow \mathcal{M}_n(\mathbb{R}) \\ X \mapsto NX - XN \end{cases} \quad \text{and} \quad \mathcal{S}^*: \begin{cases} \mathcal{M}_n(\mathbb{R}) \rightarrow \mathcal{M}_n(\mathbb{R}) \\ X \mapsto {}^t N X - X {}^t N \end{cases}$$ Show that the kernel of $\mathcal{S}$ is the set of real Toeplitz matrices that are lower triangular. We admit that the kernel of $\mathcal{S}^*$ is the set of real Toeplitz matrices that are upper triangular.