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 ...

learn more… | top users | synonyms

1
vote
2answers
42 views
+50

Derivatives of component inverse functions

I might have missed the point of the following questions. Anyone kindly give a suggestion? Let $f:\mathbb{R}_\mathbf{x}^3\to\mathbb{R}_\mathbf{y}^3$ and ...
1
vote
2answers
2k views

Singularity in matrix when inverting in Matlab

As data I get a matrix A but in my algorithm I need to work on its inverse. What I do is: C = inv(A) + B; Then in another line I update A. In the next cycles I ...
0
votes
1answer
20 views

For any continuous function f(x), how can I split up the function and restrict the domain to find an inverse?

I want to know everything there is to know about inverses for curiosity's sake. I am totally fine finding the inverse of a function where each x maps to a unique y coordinate, but when we get to ...
2
votes
1answer
32 views

What does $g(f(x))=x$ imply?

Let $f: X\rightarrow Y$ and $g:Y\rightarrow X$ be functions such that $g(f(x))=x$ for all $x\in X$. (a) Prove that $f$ is injective. (b) Prove that $g$ is surjective. (c) Give an example of a pair ...
1
vote
0answers
41 views

Operator norm of the inverse

If I made no mistake, one can calculate the operator norm of the inverse of any given (invertible) operator $A: V\rightarrow V$ via: \begin{align}\|A^{-1}\| & = ...
1
vote
2answers
24 views

Self inverting Rings

Would it be possible for a ring to have elements that are their own additive inverses? What I mean is, would it be possible to have a ring $K$ of mathematical objects $A$ such that: $$A+A=i,\;\forall ...
0
votes
1answer
25 views

Finding inverse using logs

$$ x = \left(\frac{4^y}{-2}\right)^{\frac{1}{3}} $$ i have correct answer of $\:y=\log(4)-2x^3$ i'm lost on steps to obtain the answer. i tried the ...
1
vote
2answers
26 views

Problem inverting a function

I have this function: $$v(t)=\sqrt{\frac F c} \tanh \left(\frac{\sqrt{Fc}}{m} t \right)$$ I can visually see that t=6.3 when v=27.8, so why don't I get t=6.3 upon putting v=27.8 in this supposedly ...
0
votes
1answer
69 views

Given its pseudo-inverse, is there a fast way to measure the degree of full-rankness of a nonsquare matrix?

update: I realized the core of question is about ill-conditioning of the matrix (aka Multicollinearity). In a computer, with floating point arithmetic, it is impossible to talk about full-rankness. We ...
0
votes
2answers
40 views

“Self invertible” group

Let there be an Abelian group with a binary operation $\ast$ on a set $S$. Let such a group respect the following propriety: $$ (X\ast Y)\ast Y = X$$ For any $X$ and $Y$ in $S$. I realize that by ...
0
votes
1answer
86 views

Inverse of a function

From my text book it says that $f(x)= x^3$ and $f^{-1}(x) = \sqrt[3]{x}$ , which I totally agree with. why does $f(x)= \frac 1 {x-1}$ and $f^{-1}(x)= \frac 1 {x + 1}$ and not equal $f^{-1}(x)= \frac ...
0
votes
0answers
32 views

Finding the inverse of trig functions

I'm supposed to find the inverse of $$f(x) = \cos(x)+x$$ I usually just substitute $x$ for $y$ and then re-arrange. What do I do in this scenario?
0
votes
0answers
17 views

Inverse functions determination by integral

From "Inverse functions and differentiation": Integrating this relationship gives $$ f^{-1}(x)=\int\frac{1}{f'(f^{-1}(x))}\,dx + c. $$ This is only useful if the integral exists. ...
0
votes
0answers
22 views

multiplicative inverse in factor ring

If I need to find the multiplicative inverse of an element in some $T[x]/(m)$ factor ring, do I need to solve a diophantine equation to get the solution? Let the element be $f$. Then $fu \equiv 1$ ...
0
votes
2answers
22 views

Find the inverse of the function

Find the inverse of the function $f(x) = -2 \cdot4^{2(x-3)} - 1$.
-1
votes
0answers
30 views

Matrix of Expectation of Random variables Update [closed]

I am not a math guy, but here I have encounter a problem about finding an inverse matrix, which the original matrix are elements of expectation of random variables. I think it is an optimization ...
3
votes
2answers
109 views

Conditions for a matrix to be invertible

Let $n \geq m$ and let $C$ be a $n \times m$ full rank matrix, that is $rank(C) =m$. Considering that $D$ is a diagonal positive semidefinite matrix, under which conditions is the $ m \times m$ matrix ...
2
votes
1answer
40 views

How to invert a matrix

I would like to disprove the following claim, that seems false to me, finding a counterexample. Let $\mathbf{A}, \mathbf{B} \in \mathbb{R}^{n \times k}$, for $k < n$. Let us assume that $rk(A) ...
1
vote
1answer
26 views

Is there a pseudo inverse $X$ such that $ABX=A$?

Question The title pretty much sums it up. I need to find a matrix $X$ such that: $A B X = A$, with $A\in R^{n\times n}$, $\text{rank}(A)=n$, $B\in \mathbb{R}^{n\times m}$ given. The matrix $X$ ...
0
votes
1answer
27 views

Number of configurations in a constrained nested loops and configuration back from serial

Consider 4 counters looping the digits 0, 1, 2 to form the various "configurations", like in : ...
3
votes
1answer
40 views

Is there a faster way to calculate a pseudo-inverse of a matrix than using SVD that is as numerically stable as with SVD?

Is there a faster way to calculate a pseudo-inverse of a matrix than using SVD that is as numerically stable as using SVD?
15
votes
12answers
2k views

Why is $\frac{1}{\frac{1}{X}}=X$?

Can someone help me understand in basic terms why $$\frac{1}{\frac{1}{X}} = X$$ And my book says that "to simplify the reciprocal of a fraction, invert the fraction"...I don't get this because isn't ...
0
votes
0answers
26 views

Using IFT to determine whether $f:(x,y)\longmapsto\left(\frac{x^2-y^2}{x^2+y^2},\frac{xy}{x^2+y^2}\right)$ has inverse function near $(0,1)$

Well, we can say $f(x,y)=(u,v)$. We want to determine whether there is a function that describes $x,y$ in terms of $u,v$. Define ...
0
votes
2answers
16 views

Extended Euclidean Algorithm for Modular Inverse

I'm currently learning how to find the inverse of a modulo with the Extended Euclid Algorithm and I stumbled upon a problem when finding an inverse when the $m>p$ as for $m \equiv 1 \pmod{p}$ For ...
1
vote
1answer
21 views

Nonsingular block matrix

Let us consider a matrix $\mathbf{A} \in \mathbb{R}^{n \times n}$ and the block partitioning $$ \mathbf{A} = \begin{pmatrix} \mathbf{A}_{11} & \mathbf{A}_{12} \\ \mathbf{A}_{21} & ...
1
vote
2answers
29 views

Inverse modulo function

How can we calculate the inverse of a modulo function, now I have a problem given me $f(n)=(18n+18)\mod29$, need find inverse of $f(n)$ ? how is the process to do it?
0
votes
1answer
54 views

Solution of matrix equations

$$A=\begin{bmatrix} 3 & -2 & -1 \\ 1 & 2 & 1 \\ -1 & 1 & 1 \end{bmatrix}, X= \begin{bmatrix} x \\ y \\ z \end{bmatrix}, B = \begin{bmatrix} 1 \\ 7 \\ 2\end{bmatrix}$$ ...
0
votes
2answers
34 views

How do I calculate the inverse of these matrices?

In learning how to rotate vertices about an arbitrary axis in 3D space, I came across the following matrices, which I need to calculate the inverse of to properly "undo" any rotation caused by them: ...
2
votes
0answers
65 views

Is this a field of study?

Is there a name for an equation that takes the following form? $$F(f(x),f^{-1}(x),x)=0$$ A nice example being $$f(x)-f^{-1}(x)=0$$ because the solutions of this equation are their own inverses. ...
2
votes
3answers
99 views

Why is a matrix $A$ that fulfils $AA^t = I$ invertible?

Given a square matrix $A$ that fulfils $$AA^t = I$$ Justify why must $A$ be invertible. The answer, according to my book, is simply $$AA^t = I$$ $$A^t = A^{-1}$$ I don't ...
1
vote
1answer
27 views

number of flops required to invert a matrix

I have a n-by-n upper triangular matrix R and I can calculate it's inverse by back substitution. I cannot make myself see why it needs $O(n^{3}/3)$ flops to do so. Can you explain?
0
votes
0answers
13 views

calculating the inverse of an upper triangular matrix

I've been given this hint that if we have an upper triangular n-by-n matrix $R=\begin{bmatrix} \alpha & v^{T}\\ 0 & S \\ \end{bmatrix}$ then $C=(R^{T}R)^{-1}$ can be computed as ...
7
votes
3answers
228 views

Which is easier to work out: determinant or inverse?

Suppose $A\in M_n(R)$ be a $n\times n$ matrix over some ring $R$. Which of the following two tasks is easier? to work out $\det(A)$; to work out $A^{-1}$. More specifically, I want to know the ...
1
vote
2answers
161 views

If a matrix is not invertible, is it still possible to find a left and/or right inverse?

I was recently asked to find the right inverse of some matrixes. I found that all three of them were invertible, so it was just a matter of finding their inverses, which would be exactly the same as ...
2
votes
2answers
18 views

About inverse matrixes

I've been reading about invertible matrixes. I have a few questions: One theorem says The rank of an invertible matrix of size $n$ is $n$. So, is it safe to say that all invertible matrixes ...
0
votes
4answers
27 views

Inverse $2^{18}$ in GF(23) without extended euclidean algorithm

I have a little question about the calculation of the inverse of $2^{18} \mod\ 23$. I have the solution of this: $$ \text{The inverse of $2^{18}$ is $2^{-18}$. The modulus in the exponent is ...
0
votes
1answer
51 views

How to prove that a matrix inverse is invertible?

First off, I'm trying to prove that $(A^{-1})^{-1} = A$, but in my proof, I assume that $A^{-1}$ is invertible. I'd like to see or do a proof that $A^{-1}$ must be non-singular, but I'm stuck at ...
2
votes
3answers
121 views

Inverse of inverse of function?

What is the inverse of inverse of a function (I assume the original function is invertible)? Is this the original function? Is it always true?
2
votes
3answers
2k views

How do we find the inverse of a function with $2$ variables?

$$f(m,n) = (2m+n, m+2n)$$ What do we have to do to find the inverse of this function? I don't even know where to begin.
0
votes
0answers
17 views

inverse function as a differential equation

let be the functional equation $$ f^{-1} (x)=g(x) $$ (1) where $ g(x)$ is known but $ f(x) $ is not my question is if i can rewrite (1) as the solution of a certain nonlinear differential equation ...
1
vote
2answers
18 views

How do I find the inverse of this exponential function?

$x=-3(3^{-x})+9$ I know the steps up until a certain point. $x=-3(3^{-y})+9$ $x-9=-3(3^{-y})$ $\frac{(x-9)}{-3} = 3^y$ $ln (\frac{x-9}{-3}) = -y * ln 3$ Not sure what to do from here. I know I ...
1
vote
1answer
43 views

the rank of a matrix and its inverse are always equal

I had a true or false quiz in a linear algebra course, one of the statements read the rank of a matrix and its inverse are ...
0
votes
0answers
21 views

Inverse Supply Function

Efficient small firm with cost function $c(q) = qe^{0.5q}$ $0< q \leq 10$ where $q$ is the number of units produced. Determine the firm's inverse supply function.
1
vote
1answer
45 views

What does it mean when a matrix is to the (-1/2) power?

I'm reading a machine learning paper that uses a form of matrix normalization called symmetric divisive; given a matrix A and a diagonal matrix D derived from A, we define $$N=D^{-1/2}AD^{-1/2}$$ I am ...
3
votes
3answers
43 views

Yet another inverse function to calculate

Is it possible to evaluate the inverse of this function, in order to obtain for each $y\in\mathbb R^+$ an explicit value of $f^{-1}(y)$? Thanks in advance! ...
0
votes
1answer
26 views

Hard time with Derivatives of Inverse Functions

I'm having a really hard time with this question I keep googling for advice but can't find anything solid that's similar! Please help. I'm not sure if I should derive first or find the inverse first? ...
0
votes
1answer
41 views

Where exactly is the following process incorrect to yield an impossible answer

I was playing with my calculator and found some strange phenomena. $\cos(\tan(\tan(\tan(\pi/4)))) = 0.75686700166$ Verify here Now when we apply some inverses, then $\tan(\tan(\tan(\pi/4))) = ...
0
votes
2answers
40 views

Linear Algebra Review Questions

So I have a test on Monday and my professor posted a couple of non-graded review questions that she said we should look over. Anyhow, I have a couple of questions that I'd like answered if that's ...
0
votes
0answers
17 views

Inverse Rotation - Original X / Y values

Really stumped. I'm currently writing a program and I am given a rotated rectangular object on a 2d plane. The object has been rotated about it's center point and I need to find out how to get the ...
1
vote
1answer
76 views

Determining the values of k for which the Matrix A has an inverse

I've been given this question in class, with the 3x3 matrix: 2 1 0 1 2 1 0 -3 k My job here is to find the values of k for which this matrix has an ...