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John D'Errico


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Retired

5,446 total contributions since 2006

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

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Answered
Error using ==> asind Argument should be real.
So what is the problem? It seems the error message states exactly what happened, and why MATLAB sees a problem. Honestly, it ju...

2 hours ago | 1

Answered
how do I right x^2 in MATLAB
Is x a scalar? If so, then you write it as x^2. Is x a vector? Then, assuming you want to perform an element-wise squaring, yo...

22 hours ago | 0

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Answered
4D Interpolation scattered Data
Sorry, but you cannot use tools like griddata or scatteredInterpolant to interpolate non-single valued relations. It seems all y...

24 hours ago | 0

Answered
How to draw a 3D circle that is tangent to two lines
First, if the lines are in the same plane, then you can pretend this is a problem in 2-dimensions. You can always rotate everyth...

24 hours ago | 0

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Answered
Determinant of a unitary matrix
Gosh. I wonder, if there were really much better ways to compute the determinant, they might have used it? ;-) There are no spe...

1 day ago | 0

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Answered
How to remove duplicates from a matrix without using unique?
How could you use the output of a sort to help? Why not make an effort?

1 day ago | 1

Answered
Can anyone tell what is this line doing
You asked again, why you cannot use f(1,3), instead of f(1,2). LOOK CAREFULLY AT WHAT YOU HAVE. TAKE IT ONE STEP AT A TIME. f...

1 day ago | 0

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Answered
Create Random Points in Elliptical Belt
If you already know how to generate random points uniformly over an elliptical region, then you already have the simple answer. ...

1 day ago | 0

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Answered
Exponential distributed random values
You need to do that since your exponential rate parameter varies. If it were constant, this would not be necessary. The first a...

2 days ago | 0

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Answered
How can I solve the determinant of large-sized symbolic matrix: det(A)=0?
First, you don't want to solve for a zero determinant! Period. This will never be a well-posed problem, simply because we can tr...

2 days ago | 0

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Answered
Composite Simpson's 1/3 rule code error
Tell me, what is fx? fx is NOT a function. It is a scalar, vector, or array. Whatever x was, fx is the same thing. If it NOT a ...

3 days ago | 0

Answered
Creating a Matrix of random numbers
randi([0 1],20)*2 - 1

3 days ago | 1

Answered
excluding a small combinations from a combination?
There are not that many combinations that include the subset [2 4 6] out of nchoosek(1:10,4). This means the oversampling will n...

3 days ago | 0

Answered
How to plot a complex function in matlab like : f(z)=sin(z)?
The problem is, if z is a complex variable, then so is the extension of sin(z) into the complex plane. For example... sin(1 + i...

3 days ago | 1

Answered
Integration of a function
It can be confusing at times I have seen for newcomers to know which tools apply where, because we have symbolic tools and numer...

3 days ago | 0

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Answered
what does this line do
It does nothing on its own. A single line of code has little meaning, out of context. What does it do? It sets some elements o...

4 days ago | 0

Answered
Matlab solver for natural log equation
Does a solution near(er) to zero exist? PLOT IT!!!!!! syms x f = (-27109/x)-0.95*log(x)+25.18 - log(0.5); fplot(f,[10,1000]) ...

4 days ago | 0

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Answered
Is NaN ok here?
Sure. It does not bother me. Why does it bother you? B = [1.66000000e-01 6.60000000e-02 1.40000000e-02 3.90000000e-02 1.4000000...

4 days ago | 0

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Answered
Gaussian Quadrature Error Help
I think you misiunderstand Gaussian quadrature. You claim to have 4 points. WRONG. You have TWO points in x, and TWO in y, the...

5 days ago | 1

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Answered
Tic, Toc Behavior
Using tic and toc to masure any time is a bad idea. Using tic and toc to masure any time is a bad idea. Using tic and toc to m...

5 days ago | 1

Answered
What does squeeze() do in MATLAB?
Squeeze is a useful tool to help compress dimensions of a multidimensional array when you have performed some operations. Let me...

5 days ago | 1

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Answered
Solve as Optimization Problem in Matlab
In MATLAB, the solution is intlinprog. Of course, there may be multiple solutions. intlinprog does not give them, if any could e...

6 days ago | 0

Answered
Matrix multiplication from the right with inverse matrix
a is a 3x2 matrix. No matter what, you cannot compute the inverse of a, so U=R*A^-1 is meaningless. I assume you want to sol...

6 days ago | 0

Answered
Look-up Table "Newton Interpolation"
Let me suggest this is a bad idea. The result will be an interpolant that is not even differentiable across the data points. A n...

7 days ago | 0

Answered
radius and height of a cylinder with given volume and cost per m^2
I won't do your homework for you, and I truly hope nobody else does it either, as that would be inappropriate. But it seems if ...

7 days ago | 1

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Answered
How to do a non linear fit in MATLAB?
Only VERY poorly. Your data is barely sufficient to estimate anything more than a straight line. R=8.314; P=[0.1 0.1 0.1 0.1 ...

7 days ago | 0

Answered
Fit with exp2 doesn't working
I'll assume you want to fit this using a sum of two exponentials? Since that is the way you plotted it, I assume that is so. ...

7 days ago | 1

Answered
Curve is not fitting
With only one or two points where the function is not essentially constant to within the noise of the system, a good fit will be...

7 days ago | 1

Answered
How can i find equilibrium points of 2 ODEs?
You have a system of ODEs. An equilibrium point is where the derivative is zero. So just use solve, applied to the derivatives...

7 days ago | 0

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Answered
Use or Pi and raising matrix to a Power
MATLAB tells you exactly what is wrong, and how to fix it. (This has nothing to do with your use of pi.) Error using ^ (lin...

7 days ago | 0

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