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# John D'Errico

### Retired

5,033 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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Howto Replace Specified and Non-Specified Elements in Matrix with Strings
You cannot do so. Sort of. Ok, well, you can. sort of. A double precision matrix in MATLAB is a rectangular array that contains...

5 hours ago | 1

Solving an Incomplete Matrix such that A*transpose(A) = eye(n)
There exist NO such values for a,b,c such that A*A' == eye(3). Look carefully at A*A'. vpa(A*A') ans = [ ...

19 hours ago | 2

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Problem of color interpolation of surf plot
This is an interpolation artifact. The cause is a pretty simple one. Fixing it is slightly less trivial, because you need to und...

1 day ago | 0

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How to extrapolate the plot of continuous data points so as to extend the region of plot
“In the space of one hundred and seventy six years the Lower Mississippi has shortened itself two hundred and forty-two miles. T...

1 day ago | 0

How do I create a polygon with n sides with only 90 degree or 270 degree internal angles?
I guess I don't really see the problem. And I don't really see where you are going with this, but... Start with a library of ev...

1 day ago | 0

Golden Section Search algorithm, golden number why is 0.381
I think you need to spend some time in class listening, lol. Or, maybe your instructor did not explain this. It is very possible...

2 days ago | 2

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"temp" was previously used as a variable, conflicting with its use here as the name of a function or command.
The MATLAB language does not include this syntax temp += 26 Just because it works in some other language, does not make it va...

3 days ago | 0

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"Scattered Interpolant" produces invalid values
I can shed light on your problem. What you think of as extrapolation is different from the way scatteredInterpolant sees the con...

3 days ago | 1

FZERO requires at least two input arguments
However you got the code you wrote, much of it is not valid syntax in MATLAB. This line, for example: fzero ltol = 10^-14; mid...

3 days ago | 0

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Contour plot ignores a set of data points
I've moved what was a comment into an answer, then added a bit... A very simple example of what I described is shown here: px ...

3 days ago | 1

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solve integral using ode45 (by derivative)
While what Ameer wrote looks like it will work, it still uses the dreaded & disallowed integral function. I'm adding this answer...

4 days ago | 1

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How can I PERMANENTLY change the path each time MATLAB is opened?
help savepath As well, if you were setting the path using pathtool, there is an option to SAVE the path. This leaves only the ...

4 days ago | 0

No. the code gives the correct answer in terms of what you wrote. That the code you wrote does not solve the problem you want to...

4 days ago | 2

how to know if two lines are intersected ?
Just find the point where the lines are at their closest approach. If the point of closest approach is zero, they intersect. Gi...

4 days ago | 1

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Finding zero crossing of equation
Are you trying to solve for a zero crossing of f(x)? if so, then computing the derivative is irrelevant, unless you might want t...

5 days ago | 0

Estimate best parameters using lscurvefit
You are getting lost and confused by the names x and y. They are irrelevant. You have 3 parameters. You have 5 data points, numb...

5 days ago | 0

Scaling a vector-valued non-linear function-numerical optimization
To a large extent, I want to disagree with Michael in his recent comment, except that he is correct, in that a perusal of the gr...

5 days ago | 0

FMINCON Linear Constraint Strictly Greater/Less Than
You cannot easily do so. fmincon assumes that the constraints do allow the bounds as possibilities. In fact, fmincon allows the ...

5 days ago | 0

Generating random Gamma distribution
The trick is to understand how a transformation can solve the problem. This is a standard way to produce random numbers with som...

7 days ago | 0

can't plot exp * sin graph
Your problem lies in not understanding the difference between the .* and * operators. (In fact, this was probably why you were a...

7 days ago | 2

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whats wrong with my code
I wouldstart by saying this is not how you define a function. function fact[a,b,c]=my_fact(x) That is not valid syntax to defi...

8 days ago | 0

Simple Code working in the Command Line but not through function
You change grad inside nnCostFunction. But do you RETURN grad? No. What arguments do you return? J = nnCostFunction(nn_params, ...

8 days ago | 0

Im trying to solve an equation that have variable on left and right side
How is depth relevant to anything here? It does not appear in the expression. Maybe I'm just not thinking very "deeply" today. ...

8 days ago | 0

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How do I solve this equation?
I've added a separate answer here only to explain how you would have used dsolve, and then how you would plot the solution. You...

8 days ago | 0

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Local Minimum possible - exit flag 2 - Non linear optimisation problem with Non-linear constraints.
Setting the tolerances to some absurdly tiny number is something I frequently see people do. It almost never seems to improve th...

8 days ago | 1

Explicit solution using Syms tool box
You WANT to find a solution to a general 12'th degree polynomial. There are things I want, but cannot have either. In this case...

9 days ago | 0

Generate a vector under norm condition
As long as you are willing to specify that the vector is normally distributed under a constraint, you can do this. In fact, it i...

9 days ago | 1

Creating 3d surfaces from two independent functions
Why is this not just f3 = @(x,y) min(f1(x,y),f2(x,y)); You want the result which is the smaller of two functions. In your ex...

9 days ago | 0

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I can't solve this nonlinear equation
You have too many equations, too few unknowns. 8 equations, with 9 unknowns. This is often called an under-determined problem. ...

9 days ago | 0

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