Inversion is the process of creating the opposite. Familiar examples include multiplicative inverse $2 \mapsto 1/2$, inverting functions $f(x) \mapsto f^{-1}(x)$, matrix inverse $M \mapsto M^{-1}$ etc. Please include an additional subject tag such as (linear-algebra) or (arithmetic) to help clarify ...

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Example of sets $A$ and $B$ and functions $F$ and $G$ such that $F: A \rightarrow B, G: B \rightarrow A, G \circ F = I_{A}$, and $G \neq F^{-1}$

Give an example of sets $A$ and $B$ and functions $F$ and $G$ such that $F: A \rightarrow B, G: B \rightarrow A, G \circ F = I_{A}$, and $G \neq F^{-1}$ I was thinking maybe $F$ can be a function ...
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Inverse of a 4x4 matrix with variables

I missed my class on the inverses of matrices. I'm catching up well, but there's a problem in the book that got me stumped. It's a 4x4 matrix that is almost an identity matrix, but the bottom row ...
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27 views

Simplify functions involving modular arithmetic

In this question, the answer says that f o g(x) = x. But I am unable to get this result. The expression I am able to get is that f o g(x) = 7*(x mod 3) + 57*(x mod 7) (mod 21). I am unable to ...
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47 views

Inverse Laplace transform of ratio of polynomials

I would like to understand if the inverse laplace transform of these functions gives something in terms of known functions (such as exponentials..see my examples). ...
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1answer
31 views

Inverse of function arcsin

I'm having trouble finding the solution of the inverse of the function ${\rm f}\left(y\right) = \arcsin\left(\,3 - x2\,\right)$ Isn't $\arcsin$ the inverse of $\sin$ ?. This is what I have now as ...
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1answer
26 views

Parametric Curves Existence of Tangent

If $\frac{dy}{dt}$ and $\frac{dx}{dt}$ exist, then does $\frac{dy}{dx}$ always exist when $\frac{dx}{dt} \not=0$? Indeed, this is a very simple question. Sorry but I'm just a beginner for ...
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1answer
49 views

How to calculate the inverse of the line integeral.

Let $f$ be a polynomial function, $$ f(x) = a_0 + a_1 x + ... + a_d x^d $$ where $a_0$, $a_1$, ..., $a_d$ are parameters and usually $d \le 6$. Let $g$ be the line integral of $f$, $$ g(x) = ...
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120 views

Finding inverse of a matrix

This question is in my assignment. We are not allowed to use any symbol to represent any elementary row and column operations used in the solution. We must solve it step-by-step. Please help me to ...
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1answer
87 views

Inverse function, power set.

How to prove, that for every function $F: P(\mathbb N) \rightarrow P(\mathbb N)$, where: $F(\mathbb N)=\mathbb N$ $F(\emptyset)=\emptyset$ $F(\bigcup \Xi)=\bigcup\{F(X)|X\in\Xi\}$ for every $\ ...
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1answer
111 views

Inverse of Positive definite matrix

Assume $P$ is a non-negative positive definite matrix. It is well known what $P^{-1}$ is also positive definite and thus all its diagonal entries are positive. Can we say something about the off ...
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98 views

Calculating $\text{erf}^{-1}(z)$ for $z\in\mathbb{C}$

All the information I found about inverse error function $\text{erf}^{-1}(z)$ was about $z\in\mathbb{R}$. Also I found some Taylor expansions for it, but as the function is unbounded near $z=\pm1$, ...
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44 views

Injective and Surjective Functions on Sets

I'm fairly new to math proofs. I've been looking for some counterexamples to the following theorems, especially the second one. I haven't been able to think of a scenario. Are the following theorems ...
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1answer
48 views

Finding the Inverse Laplace transform using the Step and Shift theorems

I want to find the Inverse Laplace Transformation of the function given above. I used the step and shift theorems to come up with an answer. Can someone simply verify the answer. This is my first ...
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221 views

From matrices to bipartite graphs

Assume $G(A,B)$ is a bipartite graph and assume $L(G)$ is the adjacency matrix of its line graph. define $$B=[3\text{I}+L(G)]^{-1}$$. Is it always the case that for each edge $e=(a,b)\in G$, we have: ...
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337 views

Simple to state yet tricky question

Define $$A=\left[\mathrm I+\sum_{k=1}^{m_1}v_k v_k^T+\sum_{k=1}^{m_2}u_k u_k^T\right]^{-1},$$ where each $u_k$ and $v_k$ is a $0$-$1$ column vector, and for each $1\leq i \leq n$, the $i$th component ...
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759 views

A square matrix A is invertible if and only if det A ≠ 0. Use the theorem above to find all values of k for which A is invertible

$$\begin{pmatrix} k & k & 0 \\ k^2 & 25 & k^2 \\ 0 & k & k \end{pmatrix}?$$ I did a sample question before this one: $$\begin{pmatrix} k & k & 0 \\ k^2 & 16 & ...
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Tricky question in Matrices! [closed]

Define $$A=[\text{I}+\sum_{k=1}^{m}u_{k}u_{k}^T]^{-1}$$, where for each $u_k$ is a $0-1$ column vector. Prove that for every $1\leq k \leq m$ $$Au_{k}u_{k}^T\geq0$$ i.e. each entry of $Au_ku_k^T$ ...
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1answer
62 views

Laplace Transformation spring question

Here is the question: http://i.imgur.com/XAH2UnX.jpg I can't seem to get the answer. Are those values in the writing like 1N/m even relevant? Can someone give me some direction? Thanks!
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42 views

Ultrametric matrices and their inverse

A non-negative square matrix $A$ is ultrametric iff: $A(i,i)>\{A(i,k),A(k,i)\}\forall k,i$ $A(i,j)\geq\min\{A(i,k),A(k,j)\}\forall i,j,k$ It is well-known that the inverse of non-negative ...
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878 views

Is $A + A^{-1}$ always invertible?

Let $A$ be an invertible matrix. Then is $A + A^{-1}$ invertible for any $A$? I have a hunch that it's false, but can't really find a way to prove it. If you give a counterexample, could you please ...
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1answer
60 views

Calculating Inverse function

Please help me with the following question: Calculate, if possible, the inverse of the following functions: (i) $f(x) = (2x - 2)^5$ (ii) $f(x) = (2x - 3)/4$ (iii) $f(x) = x^2 + 1,$ for $ x \geq ...
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Conversion of roots of a polynomial

I'm wondering, given a polynomial $P(x)$ with roots $r_i (1\le i\le n)$, how to determine the polynomial $Q(x)$ such that its roots are $r'_i=f(r_i)$. For example, if $P(x)=x^2-x-6=(x-3)(x+2)$ and ...
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If $g(x)=3+x+e^x$, then how do I find $g^{-1}(4)$?

If $g(x)=3+x+e^x$, then how do I find $g^{-1}(4)$? I took $g(x)=y$ and tried to solve the problem, but i could not get the solution.So, please help me by providing me the solution to my question.
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Can I find the Pseudoinverse (Moore-Penrose inverse) just by knowing the one-sided inverses of a matrix?

Consider a matrix such as $B = \begin{bmatrix} 1 & 0 & 2 \\ 0 & 1 & 1 \end{bmatrix}$. I know how to compute the right inverses (or in the case of $m\geq n$ the left inverses) and ...
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157 views

What is the inverse function of $f(x)=x/(1-x^2)$

Can you give me a hint for how the inverse function of $f\colon (-1,1)\to \mathbb{R}\colon f(x)=\frac{x}{1-x^2}$ looks? I need to show a homeomorphism!
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1answer
322 views

Trick: Substitution in inverse trigonometry.

My friends say, it is some what difficult to know, which trigonometric function has to be substituted in the inverse trigonometric equations, to get the correct solution. So, I thought to take up this ...
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1answer
21 views

Inverse of $\{a_1 A_1,…,a_n A_n\}$

$a_1,...,a_n\in \mathbb{R}$ $A_1,...,A_n$ are the rows of the invertible matrix A I am trying to find a regular formula for this. Is it possible? Thanks for help!
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Left inverse iff injective; right inverse iff surjective

For a function $f:A\to B$, the function $g:B\to A$ is called: a left inverse for $f$ if $g\circ f$ is the identity on $A$ (i.e., $g\circ f = {\rm id}_A$); and a right inverse for $f$ if ...
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64 views

Solution of matrix equations

$$A=\begin{bmatrix} 3 & -2 & -1 \\ 1 & 2 & 1 \\ -1 & 1 & 1 \end{bmatrix}, X= \begin{bmatrix} x \\ y \\ z \end{bmatrix}, B = \begin{bmatrix} 1 \\ 7 \\ 2\end{bmatrix}$$ ...
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1answer
89 views

Finding the inverse function

The question is to find the inverse function of $$f(x)=x-(2\sqrt{x})+1$$ I first found that the domain of definition is $\,x\ge 0$ Then studied the variation of the function and it is decreasing ...
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414 views

Showing a function is bijective and finding its inverse

The function f: ℝ2-> ℝ2 is defined by f(x,y)=(2x+3y,x+2y). Show that f is bijective and find its inverse. I've got so far: Bijective = 1-1 and onto. 1-1 if (2x1+3y1,x1+2y1)=(2x2+3y2,x2+2y2) Then ...
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1answer
70 views

derivative of product of 2 inverse matrices

I was trying to differentiate the equation below: $$ \frac{\partial a^T X^{-T}X^{-1}a} {\partial X} $$ where X is invertible but not symmetric and $X^{-T}$ means transpose of inverse of X. In the ...
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108 views

Find the inverse z-transform of $E(z)=\frac{z+1}{(z-1)(z-0.6)}$

$$\begin{align} E(z)&=\frac{z+1}{(z-1)(z-0.6)}\\ \frac{z+1}{(z-1)(z-0.6)}&=\frac{A}{(z-1)}+\frac{B}{(z-0.6)}\\ z+1&=A(z-0.6)+B(z-1) \end{align}$$ set z=0.6: $$\begin{align} ...
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32 views

About the inverse matrix of the form $(I+cH^{-1})^{-1}$.

Given $(I+cH^{-1})^{-1}$, where $c$ is a constant and $H$ is a $\mathbb{R}^{n\times n}$ matrix. Suppose $(I+cH^{-1})^{-1}$ has a inverse matrix. Is there any way to calculate $(I+cH^{-1})^{-1}$ ...
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33 views

Inverse Transformation

Consider the coordinate transformation $$ \varphi\colon\mathbb{R}^2\to\mathbb{R}^2, (x,y)\mapsto (y-\arctan(x),y+\arctan(x)). $$ To make it more easy, I set: $$ ...
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184 views

Inverse functions and tangent line

Let $f(x) = \frac14x^3 + 12x + 6$ and let $y = f^{-1}(x)$ be the inverse function of $f$. Determine the $x$-coordinates of the two points on the graph of the inverse function where the tangent line is ...
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35 views

Determinant after rank 1 update of a singular matrix

The rank-1 update to the inverse of a matrix and rank-1 update to the determinant of a matrix are closely related. I would like to compute the determinant of a rank-1 updated singular (rank-1 ...
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42 views

differentiate of an inverse function of mixed exponential and algebraic form

Let $f(x)= e^{2x} + x^5 + 1$ Find $(f^{-1})'(2)$ Find $(f^{-1})''(2)$ There is a missing link in my brain with regards to dealing with a function containing exponential and algebra. :/ I'm ...
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140 views

How can we derive pseudo inverse of a matrix from its Singular value decomposition?

For a matrix $M$ with its singular value decomposition $UΣV^T$, the pseudo inverse of $M$, i.e., $M^+$ is $VΣ^+U^T$. How can I derive the pseudo inverse(Moore–Penrose) $M^+$ from the singular value ...
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Multiplicative Inverses in Non-Commutative Rings

My abstract book defines inverses (units) as solutions to the equation $ax=1$ then stipulates in the definition that $xa=1=ax$, even in non-commutative rings. But I'm having trouble understanding why ...
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Composition of function with it's inverse on subdomains

I have a short question. We have to check the following statements and tell for which one the equal sign holds. Let $M \subset \mbox{domain } f$ and $N \subset \mbox{Im } f$. ...
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221 views

Calculus inverse tangent line

Question is: Let $ f(x)=(1/2)x^3+6x+4 $ and let $y=f^{-1}(x)$ be the inverse function of f. Determine the x-coordinates of the two points on the graph of the inverse function where the tangent line ...
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184 views

Operation counts for algorithm using Gaussian elimination to find A^(-1)

I need help determining the operation counts of my algorithm that uses Gaussian elimination to find the inverse of a matrix. Can anyone help me? Here is my algorithm: ...
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1answer
60 views

3-D function that follows an inverse square law, but has an overall integral equal to a constant

I'm currently trying to figure out a 3D function which follows the "inverse square law" along any given ray drawn from 0,0,0 coordinates, but whose -inf..inf integral over all arguments converges. ...
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67 views

Delta function that obeys inverse square law outside its (-1; 1) range and has no 1/0 infinity

Does anybody know if such function exists? As I understand it, the function $$\frac{1}{x^2}$$ itself could be used as a delta function if it had no 1/0 infinity. That is why I'm in a search of an ...
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810 views

Solving System of Congruence using Chinese Remainder Theorem

I'm trying to solve a system of congruence using CRT $$x≡2\pmod3\\ x≡3\pmod5\\ x≡2\pmod7$$ My approach is First calcuating $m_1,m_2,m_3$ then M followed by inverses of $m_1,m_2$ and $m_3$ and ...
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72 views

A question about similar matrices: $Id$ and $-Id$

Currently, I'm trying to understand the idea of matrix similarity. As a toy example, I am thinking about $Id$ and $-Id$. Now, I do not think that these matrices are similar, and here is my proposed ...
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212 views

Finding the inverse of the sum of two symmetric matrices A+B

Consider calculating the inverse of matrix sum $$A+B$$ where A is a symmetric dense matrix while B is a symmetric block diagonal matrix. I am interested in finding an efficient approach to update ...
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1answer
199 views

Inverse Laplace Transform for $F(s) = (9s-24)/(s^2-6s+13)$

Find the inverse Laplace transform of $\displaystyle F(s) = \frac{9s-24}{s^2-6s+13}$. I have tried factoring out a $3$ from the top and putting it into the form of $\displaystyle\frac{b}{(s-a)^2+b^2}$ ...
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1answer
37 views

Updating eigen decomposition for a matrix after some row changes

Let us say we have a matrix $A$ which has eigen decomposition $$A=UDU^{-1}$$ If some of the rows of A are changed by multiplying a constant positive value, is there a simple way to update the eigen ...