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John D'Errico


Last seen: Today

Retired

5,717 total contributions 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.

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Answered
Numerically solve differential equation
This is just a parabolic PDE, assuming that Bi is a KNOWN constant. You just say it is constant. But you should be able to use ...

23 hours ago | 0

Answered
3D best fit curve from x,y and z data points
You may think it is easy, if only you can find someone who has the magic touch. Sorry, but not so easy. If the curve is presum...

2 days ago | 1

Answered
HOW TO GET THE VALUES OF CONSTANTS
Please don't YELL! Next, NEVER define pi. pi already exists, and I hate to tell you, it ain't 3.14. That only happens in certai...

2 days ago | 0

Answered
Code help on Euler's method
What you need to understand is that Euler is a poor method to use. Easy to write, easy to understand. But is it good? NO. And th...

4 days ago | 2

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Answered
Can I change a 3-tensor into a matrix by indexing with a matrix?
A = randn(4,4,3) % Not very creative in making up numbers. So sue me. :) [~,I] = min(abs(A),[],3) What is I? For every combina...

4 days ago | 1

| accepted

Answered
Newton Raphson Method not solving
This answer is here just to add some information. I try to teach that one should always plot everything, then look at what they ...

5 days ago | 0

Answered
How do I fit along the curve.
Why would there be code written to do something completely strange? Well, perhaps I should not call it strange, but your idea of...

5 days ago | 0

Answered
Interpolation error for one column increasing and one column decreasing
This is impossible to answer, since what you show is clearly not what you have. The error that is given indicates the vector (x...

6 days ago | 1

Answered
How can I test a long function in Matlab?
Don't test your long function. Because you should be writing SHORT functions. Then you can test each piece, verify it works as d...

6 days ago | 0

Answered
Simple limit returning NaN: f(x) = exp(-1/x)
Think of it like this. For a limit to exist at x==0, it MUST have the same limit as x approaches 0 from above, as it does when x...

6 days ago | 1

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Answered
Continuity of a function in a interval
It may seem basic to you. However, that just means you need to understand computing and floating point arithmetic. Nope. In fac...

7 days ago | 0

Answered
How to stop MATLAB from opening every time I switch on my computer?
This is not MATLAB that is your problem, but your MAC, and what you apparently told it to do. :) You have MATLAB set as a start...

7 days ago | 0

Answered
understanding "<" operator line
In order to understand this, I'd STRONGLY recommend you do the MATLAB Onramp tutorials. Try some examples. Look at what happens!...

8 days ago | 0

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Answered
Logical indexing of table failing
No. You do NOT know it contains 0.35. In fact, MATLAB cannot represent 0.35 exactly in floating point arithmetic. This is for th...

8 days ago | 0

Answered
Summing using simspons rule for a given range
If I might suggest, your goal is actively a poor one. Why? Simpson's rule is a higher order rule. It tries to give you a higher...

9 days ago | 0

Answered
Successive over-relaxation of Laplace equation is converging to slightly wrong value. Floating-point error or code error?
To understand what is happening, you need to first understand what the equations represent! Is this effectively a partial diffe...

9 days ago | 0

Answered
How can I find the eigenvalues of an n-by-n matrix using For Loops?
Simpler than what Matt has suggested is to just use matrix multiplication, coupled with deflation. That is, can you find the LA...

10 days ago | 0

Answered
Linear approximation of data set's points.
Don't do it that way!!!!!!! You cannot achieve a continuous piecewise linear function that way. Instead, use a tool designed to ...

10 days ago | 1

Answered
Matlab integration of numerical data
In order for it to be truly general, you will need to interpolate the "function". For example, we might do this: x = 0:10; y =...

10 days ago | 0

Answered
How to select complementary elements from a vector?
d = [3 2 1 5 6 7 8 9 0]; I = [1 3 7]; setdiff(d,I) Note that your example is actually incorrect, in that you claim 7 should...

11 days ago | 0

Answered
Applying Newton's Method to Sound Level Equation
Since we cannot solve it directly.... Are you absolutely positive of that? L0 = 80; beta = 32.2; L = 20; syms r solve(L0...

12 days ago | 0

Answered
Output all possible results on a 7 equation system
First, it can be proven that not all mathematical equations of this sort can be "solved". This goes back as far as Abel-Ruffini....

12 days ago | 1

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Answered
solving equations with trigonometric functions
Note that x1, x2, x5, x6 are just NUMBERS. Defining them as syms in advance does nothing. MATLAB is a language with dynamic vari...

12 days ago | 1

| accepted

Answered
error in matrix multiplication while solving system of differential equations
What you do not understand is that the exponential function is exp. Thus, instead of writing e^(-t), you write exp(-t). Next, y...

12 days ago | 0

Answered
How to solve an optimization problem over two variables using fmincon?
You CANNOT use fmincon on a problem with binary variables or any form of discrete variables. However, IF y is indeed binary, th...

13 days ago | 0

Answered
Equation to Matlab code
ALWAYS show what you wrote. Ony you know what you mean by dealing with vectors, etc. In the first case, do you have a vector of ...

13 days ago | 0

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Answered
How to calculate partial area-under-the-curve?
After all of those comments, to be honest, sorry, but you were both working far too hard on a moderately simple problem. Simpl...

14 days ago | 0

Answered
How to call fminsearch on my function
Um, you misunderstand the problem. Your function has TWO arguments. PR and PC, both of which you want to be optimized. And while...

15 days ago | 0

Answered
Uniform Random Variable PDF
What are you doing wrong? Um, pretty much everything? Sorry, but true. ;) However, you do seem to have made some credible effort...

15 days ago | 0

Answered
Solving Exponencial fuction is not returning the right answer
Yes, you THINK the true answer is 3. But it is not. format long g log(2653/2500) / log(51/50) And that is effectively the exa...

16 days ago | 1

| accepted

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