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# John D'Errico

### 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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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

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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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

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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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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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

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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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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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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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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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

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

3 days ago | 1

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

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

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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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

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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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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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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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

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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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

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

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

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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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

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

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

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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