Community Profile # John D'Errico

### Retired

Last seen: Today Active 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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Collatz Conjecture using for loop
Your code is close to a working algorithm. There are some issues truly good code would worry about. Could you ever have an over...

1 day ago | 2

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Invariably the data will vary by multiple orders of magnitude in such a problem. And that tends to imply the noise in your data ...

1 day ago | 1

Use a while loop to determine how many Fibonacci numbers are less than 100000.
What does your test do? That is... while x < 100000 Answer it tells when the INDEX of the Fibonacci number is less than 100000...

2 days ago | 0

I have a Matrix , and I want to multiply this Matrix with something so I can get zeros
Please stop posting answers when you are making only comments. In what you claim to have tried: A=[-3 6 -1 1 7;1 -2 2 3 -1;2 -...

2 days ago | 0

How to solve an equation system using a interp1-variable
interp1 is incompatible with symbolic parameters. You CANNOT use interp1 with solve. Period. So wherever you found that snippet ...

2 days ago | 0

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I have the following code to calculate d/dx sin(0.5)) using first derivative principle and compare it with the real value. Why does err starts increasing again?
What are you doing? You used a simple forward difference to compute the derivative, as an approximation to the derivative of sin...

3 days ago | 1

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The running time of binary integer linear programming and linear programming
Why is there something "wrong"? It is unexpected for you. But this just comes down to two different problems, solved by differen...

5 days ago | 0

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Matlab only calculates values for only certain inputs in a matrix.
Except that is not how to use a loop. You want to compute the inverse of each value in the array. function convof= inverseof(x)...

5 days ago | 0

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Am I understanding this correctly?
Yes. Colors that you would describe as red all have high values in the red channel, and small values in the green and blue chann...

5 days ago | 0

How to make constant to 1 in power function in curve fitting toolbox
Before you EVER make any fit to data, PLOT IT!!!!!!!! Plot your data. Then plot it in another way, until you have drained all th...

5 days ago | 0

fsolve doesn't find a solution when the value of the objective function is obtained through a Montecarlo simulation
Is your objective function a differentiable result of the parameters? If not, then fsolve cannot solve the problem. Fsol ve requ...

6 days ago | 0

How to create a vector of symbolic variables with specific labeling
The simple direct way seems easiest. v = sym('v',[1 29]); v = v([1 2 3 5 7 9 10 12 18 29])

6 days ago | 0

Unable to plot exponential graphs properly
What do you reasonably expect to happen? t varies over the interval -10 and 400. What is exp(-10)? If you don't know, then try ...

6 days ago | 0

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Plot graph of polynomials
That is not a polynomial. You have a sqrt root in there. And an absolute value. So learn how to use functions like abs, and sqr...

9 days ago | 1

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Can someone explain to me why I'm getting "Not enough input arguments" in line 2
For the simple reason that you named a function named size. Don't do this. Type this at the command line: which size -all If i...

10 days ago | 0

Solving a system of equations with arbitrary Parameter value
Look carefullly at what is returned. solution = solve(eqn_final, variable_final, "ReturnConditions", true); solution solution...

10 days ago | 0

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why PSI values are diffrent when nlmefit using ode45 solver compared to when it uses analytical solution?
There can sometimes be problems when you try to apply a nonlinear estimation scheme on top of an ODE solver. The nonlinear fitti...

11 days ago | 0

I don't know how to call my function
What language are you using here? Possibly not MATLAB. :) s = s + L*(i)^2; Do you think that squares the number i, and then mu...

11 days ago | 0

How efficient is it to use (end+1) to add a value to an array?
Increasing the size of an array incrementally is a TERRIBLE thing to do. WHY? Every time you add a new element to the end of t...

11 days ago | 1

How to use ~= operator as constraint function?
For which solver? This is a 1-variable problem. If you want help, it does help if you explain more than you have done. Note tha...

11 days ago | 1

solve efficiently sparse large linear system of equations
The fact is, a 3kx3k system is not that slow to solve. So unless you are doing this solve many thousands of times, keeping it sp...

11 days ago | 0

Matlab envelope function help
Seems pretty easy. Read the help, and look at the examples. Envelope is part of the signal processing toolbox. t = linspace(0,5...

13 days ago | 0

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Solving equations for Variable/Variable
No reason you cannot do this: syms A B C D E eqn = (A*B*C)/E == D; syms CoverD solve(subs(eqn,C,CoverD*D),CoverD)

14 days ago | 0

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Am I to understand that every function in matlab should be its own file?
Like SOME languages. Perhaps the ones you know. But certainly not all other languages. In general, yes, it is not unreasonable ...

14 days ago | 1

Find Image SVD without using SVD command
Too late for an answer to the question posed, but since the question is getting comments asking for more help, I'll post an answ...

14 days ago | 1

How to find the closed form solution of the natural and forced response of 2sin(3t) - 4x with x(0) = 0
Why do you think it is not correct? Would dsolve lie? That dsolve code must be pretty darn tricky. In fact, you have not used d...

15 days ago | 1

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parallel computing in Genetic algorithm
Whenever I see someone say they need to use parallel computing to make their code run faster, I wonder if the real problem is th...

15 days ago | 0

Solving Linear equation using LU Factorization and COLAMD
First, making a 100x100 matrix sparse is silly. Flat out, silly. The amount of time needed to solve that system is tiny, even as...

16 days ago | 0

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