Community Profile

# John D'Errico

### Retired

5,220 total contributions since 2006

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

View all

Contributions in
View by

How do I get the intersection function of 2 surfaces?
The intersection function will rarely exist as a "function". At best, it is an implicit function, thus a problem with solution l...

1 day ago | 0

ode,dsolve,spline,ode interp, differantial
You are not asking to do anything more than to integrate a spline, and perhaps to plot the result as a function of x. (You don't...

1 day ago | 0

| accepted

Integrating from polyint(p)
Sorry, but polyint cannot integrate a rational polynomial, and certainly not over an infinite region. Depending on the roots of ...

1 day ago | 0

| accepted

How to optimize matrix multiplication speed?
Do this: P = PHI*(P + Q)*PHI' + Q; While it may look exactly like the line of code you wrote, in fact, it is the same. Matrix ...

1 day ago | 0

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....

1 day ago | 0

| accepted

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...

2 days ago | 2

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:...

2 days ago | 0

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...

2 days ago | 0

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...

4 days ago | 0

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...

4 days ago | 0

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...

4 days ago | 0

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...

4 days ago | 1

| accepted

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...

4 days ago | 0

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 ...

4 days ago | 0

| accepted

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 ...

4 days ago | 0

| accepted

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...

4 days ago | 0

| accepted

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*...

4 days ago | 1

| accepted

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,...

5 days ago | 1

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...

5 days ago | 1

| accepted

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...

5 days ago | 1

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 ...

6 days ago | 1

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...

6 days ago | 0

| accepted

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...

6 days ago | 1

| accepted

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...

6 days ago | 0

| accepted

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...

7 days ago | 0

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...

7 days ago | 0

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...

7 days ago | 0

| accepted

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

7 days ago | 0

| accepted