John D'Errico

Retired

Last seen: Today | Active since 2006

DON'T contact me. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting. A retired mathematician, numerical analyst, woodworker, bridge player.

Statistics

All

View badges

Content Feed

Answered
Broad confidence bound range when fitting in Matlab
Wide confidence limits are typically a symptom, a reflection of uncertainty in some form. And unfortunately, we don't have your ...

20 hours ago | 0

Answered
How to perform svd without using the inbuilt function?
Why? That is, why is SVD not acceptable? Yes, you could write a complete code to compute the SVD, without using a call to SVD. ...

1 day ago | 0

Answered
Why am I getting this error? "Array indices must be positive integers or logical values".
Is P0 a function? (NO. It is a scalar variable.) You have this: P_twitch_short(i) = P0(0.0258*(exp((stiff*RLS)))-0.0258); Did...

1 day ago | 1

Answered
How to recover jpg or RAW images?
I'd be looking at my backups. (A GREAT thing to do.) Of course, if you are asking this question, there are no backups. Before th...

1 day ago | 0

Answered
I need to smooth a 3d graph
x=1:10; y=1:21; z=[0 0 0 0 0 0 0 0 0 0; 0 0 0 0 0 -9 0 0 0 0; 0 0 0 0 -5 -7 0 0 0 0; 0 0 -10 -25 -15 -5 0 0 0 0; 0 -20 -32 -46...

1 day ago | 0

| accepted

Answered
How i can solve the problem of primitive root?
What you mistake is that a and p are represented as DOUBLES. Can you compute a number as you want to do? What happens? a = 3; ...

1 day ago | 1

| accepted

Answered
Best way to solve this non-linear equation?
dsolve is not used to solve a PDE. It applies ONLY to an ODE or a system of ODEs. help dsolve There are no symbolic solvers in...

2 days ago | 0

Answered
Empty sym: 0-by-1
Don't write a whole mess of code, withput actually thinking about whether virtially the very first (significant) line you write ...

2 days ago | 0

Answered
simpsons 1/3 rule calculating error
Before you worry about how to plot things, and compute the error, should you worry if your code is correct at all? Gosh, that ju...

2 days ago | 1

| accepted

Answered
How find the function (equation) of the fitting surface using interpolation (method biharmonic)?
This question is asked hundreds of times on the site. The answer is, there is no simple "equation" you can write down. That is t...

3 days ago | 1

Answered
What distribution is appropriate for my data?
Why would you expect a distribution like that, with a strange hump on one side to have some predefined distribution that fits it...

3 days ago | 0

Answered
Plot two functions in one diagramm with different y-axis limits
Easy peasy. x = linspace(-5,5,1000); y1 = sin(x); y2 = cos(x); y2(y2 > 0) = NaN; plot(x,y1,'b-',x,y2,'r-') ylim([-1,1]) y...

4 days ago | 1

| accepted

Answered
How to change Options of PSO during iterations?
Sorry, but no. You cannot change the options for a solver in the middle of the solve. This is essentially true for any solver. (...

4 days ago | 0

Answered
Solving Nonlinear System of Equations with 10 variables
Use fsolve. You are trying to formulate this in terrm of a symbolic variables, but fsolve is a NUMERICAL solver. So you need to ...

4 days ago | 0

Answered
i want to solve for 'L' using iteration method in MATLAB for the equation below
help fzero Consider that your question is the same as (gT^2)/(2*pi) tanh (2*pi*d/L) - L == 0

4 days ago | 0

Answered
How to find the maximum element by length without a loop?
I'm a bit confused as to your question. If you want to choose the longer of two strings, then do as @Florian Bidaud suggests. Bu...

4 days ago | 1

Answered
MatLab eig vs LAPACK
If I had to guess, you don't need to use it. A = randn(500); timeit(@() eig(A)) ans = 0.0800828164545 B = A + A'; timeit...

4 days ago | 0

Answered
How to solve 'Equation solved at initial point' with fsolve?
As is often necessary on a problem like this, it helps to look carefully at what you have. x = sym('x',[1 2]); mu_earth = 39...

4 days ago | 0

Answered
Optimization: Capacitated Facility Location Problem
First, what is the difference between the summation over i in a sum like this: sum(f(i)*yi)) and the dot product of two ve...

4 days ago | 1

Answered
im trying to solve a system of 4 nonlinear equations with 4 unknowns
x = sym('x',[1,4]) eq1 = x(1)+.17*x(1)-x(2)-x(3)-x(4) == 0 eq2 = (((x(3)^(1/2))*x(4))/x(2))-.465797 == 0 eq3 = 2*x(1)-2*x(2)-...

5 days ago | 0

Answered
Another question on eliminating for loops....
Try it. If you can't see ndgrid doing it, then look harder. :) (By the way, lower case l (L) is a really bad variable name to us...

5 days ago | 0

| accepted

Answered
How to do piecewise linear approximation from x and y points?
x = [20 60 240 480 1440 2880]; y = [0.0278 0.1626 1.8126 4.006 18.2491 44.4084]; plot(x,y,'o-') You have only 6 data points...

6 days ago | 0

Answered
How do I access an element of an array of equations
If x is symbolic, you CANNOT use it in a colon call. But in the end, you did not ask for a symbolic result, but a function of x....

6 days ago | 0

Answered
I want to build the square wave: build a 6 subplot figure to show the time domain, and use respectively 1, 3, 5, 10, 50, 500 frequencies.How can i achieve this?
Solve a problem that is too large for you to handle by breaking it up into small enough chunks to handle. Do you know how to u...

6 days ago | 0

Answered
How to get the numerical rank of the matrix in matlab?
To compute the numerical rank of a matrix, use rank. Surely that seems logical. And you even know about rank. Bu then you seem ...

6 days ago | 2

Answered
Function to solve an equation for a given variable
If it is symbolic problem, then it is trivial. Just assign those variables, subs them in, and use solve. WTP? If it is a numeri...

6 days ago | 0

| accepted

Answered
How to identify the infeasibility from the set of equality and inequality constraints
You have a scalar problem? But then, you have TWO equality constraints? So a solution will exist only if BOTH equalities are s...

7 days ago | 0

Answered
I wanna make a .mat file
help save

7 days ago | 0

Answered
Problém with graph of implicit function
If you change the value of a, then the implicit function itself changes. So you MIGHT decide to use fimplicit3. But if you need...

7 days ago | 0

| accepted

Answered
degrees of freedom chi2inv
This really should be asked on a different forum, as only barely about MATLAB, and a good answer requires teaching a class in st...

7 days ago | 0