Community Profile

# John D'Errico

### Retired

5,216 2006 이후 총 참여 횟수

(Don't contact me. I won't answer questions.) A retired mathematician, numerical animalist, woodworker, bridge player.

#### John D'Errico's 배지

모두 보기

참여 게시물
보기 기준

답변 있음
Algorithm to extract linearly dependent columns in a matrix
It is difficult to answer this. Consider a simple matrix: format short g A = rand(4,5) A = 0.73796 0.36725 0....

약 1시간 전 | 0

답변 있음
How can I create a function with random imputs? I have to create a function called tri_area that returns the area of a triangle with abse b and heigh h, where b and h are input arguments of the function in that order
I think you may be confused. I believe what is asked is for a function with ARBITRARY inputs, in the sense it can be called with...

약 2시간 전 | 2

답변 있음
The accuracy on my LSTM deep learning neural network will not exceed 62.96%
You have shown no data, so we cannot truly say if you are doing something wrong. However, it sounds as it what you are doing is:...

약 2시간 전 | 0

답변 있음
how can i get a number as an answer?
You got a number. :) I know, its net a very useful looking number. As s floating point sym, use vpa. vpa((23401992239682647381...

약 2시간 전 | 0

답변 있음
why does similar code generate complex numbers?
What, for example, are the THREE cube roots of a negative number? We can find them all as solutions to the equation syms x xs...

2일 전 | 0

답변 있음
Is there a tool for drawing diagrams that connect equations?
I don't think there is a tool in MATLAB that will take a set of equations in arbitrary order, and then create this diagram. Yo...

2일 전 | 0

답변 있음
How can ı solve this constraint optimization problem?
Many things you can do, but since this is your homework, and there are already answrs posted, I'll just suggest a couple of thin...

2일 전 | 0

답변 있음
USING MEX TO SPEED UP THE CODE
As a counterpoint, there are some issues to consider. Much of MATLAB is already compiled code, at least in the hard working part...

2일 전 | 1

| 수락됨

답변 있음
help solving differential equations
I think you have multiple problems here, now that you claim to have the correct equation. DSOLVE finds an analytical solution to...

2일 전 | 0

답변 있음
Simplifying a algebraic or numeric expression to lowest possible power
The problem is, there are multiple solutions, because sqrt is not as simple a thing as you like. syms x >> y = sqrt(x.^2) y ...

2일 전 | 0

| 수락됨

답변 있음
Install 2 instances of Matlab on the same PC
Yes, and no. I frequently have several old versions of MATLAB on my computer. Walter has many as I recall. The only issue is if ...

2일 전 | 0

| 수락됨

답변 있음
Is there any method to calculate the inverse of matrix which changed a few values?
Bruno is correct in how to solve the problem, and also SOME of the issues with it. If you use this tool multiple times, the floa...

2일 전 | 0

| 수락됨

답변 있음
wrong differential equation solution
Sorry. I don't know what you did incorrectly, but here is what I see. syms y(t) yalpha = (1/80)*(36*exp(-t) + 125*sin(t) -3*...

3일 전 | 1

| 수락됨

답변 있음
How to limit calculation precision?
There are only two standard choices in MATLAB for floating point computations, and two ways to get round the problem. That is,...

3일 전 | 1

답변 있음
Not using adtest. Like the Ford Model T, which Henry Ford sold in any color as long as the color you wanted was black, adtest te...

3일 전 | 1

| 수락됨

답변 있음
Problem of ``sprandn'': the number of nonzero elements is inconsistent with density
Bruno has already explained why sprand/sprandn fail to produce the requested density of arrays. So this answer is here only to a...

3일 전 | 1

답변 있음
How to place a number (1) in a random position in Line 1 in a matrix of zeros?
M = zeros(10,10); M(1,randi(10)) = 1; However, if you had no idea how to solve a basic problem of matrix indexing, you REALLY ...

4일 전 | 1

답변 있음
find the std of each parameter after lsqlin
There are some issues that make this a little problematic. The main issue is if lsqlin finds itself butted up against a boundary...

4일 전 | 0

| 수락됨

답변 있음
How do I remove the z variable in the polynomial equation?
What you don't understand is that IF you did what you want, the polynomial will become diffcult to use and difficult to evaluate...

4일 전 | 1

| 수락됨

답변 있음
Can one run fminsearch on grids?
No. fminsearch presumes a continuously valued function, defined everywhere. You CANNOT use it to solve discrete problems. And ev...

4일 전 | 0

| 수락됨

답변 있음
Why is 4-by-2 matrix compatible with 4-by-1 vector?
You are using .* to do the multiplication. NOT * which is the linear algebra operator. MATLAB extends the vector implicitly int...

5일 전 | 0

답변 있음
Fitting a Curve to an Uncurling Object
The curve fitting toolbox assumes the functions are SINGLE VALUED. There can only be ONE value of y for any x. If that is not tr...

5일 전 | 0

답변 있음
How fast is fminsearch over brute force? or How fminsearch deal with a local/global min?
How fast is it? Since brute force is an extremely poor method to solve anything (unless your name happens to be the incredible H...

5일 전 | 0

| 수락됨

답변 있음
How to reduce dimension of griddedinterpolant?
whos Name Size Bytes Class Attributes eff_map 500x500 2000000 double ...

5일 전 | 0

| 수락됨

답변 있음
GA vs patternsearch for Integer problem with equality constraints
An exitflag of -2 means that GA never even found a feasible starting point for your problem. A larger population size lets it ra...

6일 전 | 1

답변 있음
Can one run fminsearch for a function defined by cases?
Can you? Yes. Should you? This may sometimes be a poor idea, although it depends on the specific segment functions. Are the seg...

6일 전 | 1

답변 있음
Generating parings of numbers and the pairs must not contain the same numbers
As Bruno has said, you are looking for pseudo-random derangements. So just to add some interesting information about derangement...

6일 전 | 0

답변 있음
Int returns Int when decimals input
fw = ((k*l*vi)/c)*(((1+p*l)*vi)/c)^(k-1)*exp(-((1+p*l)*vi)/c)^k ; When k is some non-integer value, you are raising some non-tr...

7일 전 | 1

| 수락됨

답변 있음
How to solve linear programming problem?
Second answer, since the problem has now completely changed. Again, MATLAB is still totally unnecessary. Since you will probabl...

7일 전 | 0

답변 있음
Why is it the answer from MATLAB is different from the other solving software? Where did I go wrong?
Usually when I see a confused question, where someone says "help, i got a strange answer", the reason is because they were not c...

7일 전 | 1

| 수락됨