John D'Errico

Retired

Last seen: Today | Active since 2006

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A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

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I need the installer for Matlab R2010b SP1
We cannot help you. Answers does not have software, cannot supply it. The only people who would be able to help you are at MathW...

11 hours ago | 0

Answered
problem with genetic algorithm
Clearly, your constraint function is not evaluating as a real number. It is likely complex, based on the error message. (Though ...

4 days ago | 0

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fsolve stopped because the last step was ineffective
This is a common mistake I see being made. You have a problem that has symmetries in it. x(1), x(2), x(3) all play similar parts...

5 days ago | 1

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Accessing a vector form a matrix
As an example, given vectors x1,x2,x3. I'll make some up. x1 = randi(10,1,5) x2 = randi(10,1,5) x3 = randi(10,1,5) Combine t...

6 days ago | 0

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Find the variable inside the LCM argument
You have the expression: B=lcm(nrt,Nr*Nc) where the variables B and nrt are known. The unknown variable is the product nr*...

6 days ago | 1

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volume calculation from the DelaunayTri(x,y,z) function
Its not THAT hard. You compute the volume of each simplex in the tessellation. Sum the absolute values up. (Since those simplexe...

7 days ago | 1

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Answered
is there any reason for this?
Is there any reason? Well, does there absolutely need to be a "reason"? These are a set of choices, made over a period of multip...

7 days ago | 1

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Answered
find a zero of a two-variable function
A two variable function is a surface. (@Sam Chak said this, but did not take the idea to the point of completion.) But if a sur...

8 days ago | 0

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Extracting values from optimization variable and setting constraints
Are you saying you want to constraint the sum of absolute values? That is, in context of a LINEAR programming problem? This is ...

9 days ago | 0

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Answered
I am trying to do multi step math and keep returning the wrong answer
Of course it is wrong. Why did you write 72/13? Why 25/3? I think you don't understand that 8(1/3) is NOT the same thing as ...

9 days ago | 0

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Answered
Calling GA() with 10 generations 10x vs GA() with 100 generations.
Is there any difference? Of course! Make it more extreme yet. Suppose you were to stop after 1 iteration. ONLY 1. But do it 100 ...

11 days ago | 0

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Check the result if it is divisible or not
Do you understand that you are using DOUBLE precision arithmetic to compute that mod? Do you understand that 7^2026 is a number ...

11 days ago | 1

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Answered
Treating ties in a Gaussian Elimination process
Um, max does exactly that. Where is there a problem? x = [1 2 3 4 3 4 1]; [xmax,ind] = max(x)

12 days ago | 0

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Matlab editor settings: notify undefined variables
For one example of a scenario where a variable appears to be undefined, yet is properly used, consider the case of a nested func...

12 days ago | 0

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Trying to determine roots of this polynomial (Det)
k = [1750 -750 0; -750 1250 -500; 0 -500 500]; m = [75 0 0; 0 75 0; 0 0 50]; D=inv(m)*k; syms x I = [x,0,0;0,x,0;0,0,x]; La...

12 days ago | 1

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Area using trapezoidal rule
Um, this is WRONG. Basic integral calculus does NOT say a result should never be negative. You are possibly misunderstanding wha...

14 days ago | 1

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Incorrect Coefficients from Symbolic Polynomial Equation Solving
NO. You think there is a unique solution. But that is wrong. syms a1 a2 a3 a4 x; % Define symbolic variables % Define the equ...

15 days ago | 0

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How do I extract one point from a piecewise function?
You can define a piecewise function as a symbolic function. For example... syms t M_xy(t) = piecewise(t < 0, 0, t > 0, t); % N...

15 days ago | 0

Answered
Why isn't my MATLAB plot not showing up?
A STRONG suggestion is when you do something, to look at the results of your code. Don't just give up when you see nothing in th...

16 days ago | 0

Answered
Estimating SQRT of a non-negative number the long way
If you generate an error message, MATLAB stops execution. An error is a failure, and nothing gets past that. However, a warning ...

16 days ago | 0

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Finding the index k of square nilpotent matrix A
A nilpotent matrix is a square matrix A that has the property that for SOME integer power k, we have A^k is entirely zero. The s...

16 days ago | 1

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Answered
Simultaneous Constant Optimisation for Curve Fitting
Do NOT manually search through a 15 dimensional space for a solution. You are just wasting your time, and this is why tools are ...

16 days ago | 1

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How do I graph the negative portion of a square root plot?
Since in reality, you have what is called an implicit function, we want to use fimplicit. I might do it like this: fun = @(x,y)...

19 days ago | 1

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How to invert a square matrix using Gaussian elimination
I assume you are forced to use your own code for gaussian elimination here. A bad idea if you are not. NEVER write such code you...

19 days ago | 0

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Lognormal distribution parameters mu and sigma
In MATLAB, the tools that use a lognormal distribution have you provide mu and sigma in terms of the underlying normal distribut...

19 days ago | 0

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Answered
lsqlin unexpected results !!!
Unfortunately, you would have been better off using a direct least squares. That would allow us to see how well the calibration ...

19 days ago | 1

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Trying to find pi using when loops to a tolerance of 10^-4.
Many, many things wrong in your code. I'm amazed nobody else as pointed most of them out. It was a start in the correct directio...

20 days ago | 2

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Answered
how to use a variable in finite field
g = gf(3, 8) whos g g is a gf object. But g is not compatible for multiplication by a symbolic parameter. These are two indepe...

22 days ago | 0

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code for check wether the given differential function is function g(x) or g(x,y) in matlab
Easy. For example... syms x y expr1 = 2*x; expr2 = x + x*y; Now use symvar. symvar(expr1) numel(symvar(expr1)) symvar(exp...

22 days ago | 1

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Answered
can any one help me to find simple empirical model (equation) with a little parameters for this data
As an alternate model, one that employs the assumption that the curve passes through the point (0,1), can we find a different fi...

22 days ago | 0

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John D'Errico

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