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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Implementing additional constraints in assignment problems.
Is there some general function that has been written to solve this problem? No. Of course not. Why not? There is likely no uniq...

18 hours ago | 0

13x8 Matrix Cubic Interpolation
Simplest is to just read the help for interp2. It is silly to use a lower level tool when a high level tool does exactly what yo...

1 day ago | 1

Result for solve( ) with minimized number of parameters
The problme is, the "minimal" solution that you ask for is not the complete solution. You asked solve to provide a solution. How...

1 day ago | 0

How to solve set of equations with inequality using fsolve?
First, fsolve does not solve bound constrained problems. (What you have.) Second, even if it did, fsolve does not solve problem...

3 days ago | 0

Why my imaginary graph is straight line?
fplot(t,imag(i1(t)),'LineWidth',1.5) To my eyes, this does not look straight. But then I may need new glasses.

4 days ago | 0

4x4 matrix with numbers from 1 to 4 in specific order
Hint: What does flip do? Could you use it to "flip" the order of those numbers?

4 days ago | 0

I want to find the value of k
syms x1 x2 x3 x=[x1;x2;x3]; f1=x(1)^3+12*x(2)+1; f2=x(2)^9+5*x(1)-3; f3=x(2)*x(3)^2+8; Here is the matrix k. k=[diff(f1,x(...

5 days ago | 2

smooth step function with rise time
You cannot solve the problem you claim to want to solve using a simple logistic. It does not have the flexiibility to control bo...

5 days ago | 0

Automated Bisection Method on a function tan(a)-tan(b)=0
I'm sorry, but it is provably impossible to make bisection (or any scheme like it) always find all solutions of an arbitrarily c...

5 days ago | 0

Why do I see a singular matrix warning here?
The issue is not a problem with eig, except in our expectations of what eig can do. And those expecations are fueled by our expe...

6 days ago | 0

Question

Why do I see a singular matrix warning here?
I've posted this question as a "response" to a question posed by someone else, but as an answer to another question. Since I can...

6 days ago | 1 answer | 1

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Find the file number when a condition meets
Beginners do this sort of thing. They are tentative, almost afraid to use MATLAB, even when they think they need to. So they lea...

7 days ago | 0

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1D randomwalk matlab tutorial on youtube
I think you need to read things like the syntax of various tools, like while. You also need to learn the syntax of just how to w...

7 days ago | 0

Generate all possible combinations summing up to a given number
These are commonly known to mathematicians as integer partitions, thus the ways we can write an integer as a sum of smaller inte...

8 days ago | 0

How many terms of series are required to get accuracy upto three decimal point. That is series sum correct upto 3.141
@ajeet sahu - what you do not seem to understand is that the script you have shown IS performing the correct iterations, The pro...

8 days ago | 0

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Constants not recognized in integral
You are still thinking that you are using some other language, where you need to declare variables as doubles. This line does n...

11 days ago | 0

How can i write this equation: d = obs + sqrt(alfa*Cd^0.5)*randn(nd, ne)
Do I understand you correctly? obs is an array of size 51x71x3? Or is it a vector of that length? Regardless... alfa is a scala...

11 days ago | 0

Array indices must be positive integers or logical values.
It does not matter that you WANT V(0) to be something. MATLAB does not support zero based indexing. PERIOD. However, nothing st...

12 days ago | 1

plotting a for loop returns Empty Graph
You are not plotting ANYTHING in a for loop. You may think you are. Where are the plot statements? AFTER THE LOOP TERMINATES. Af...

12 days ago | 0

How to solve a large 6-variable non-linear matrix determinate equation for all unique values.
This is an almost impossible problem to solve symbolically. Why? symbolic computations using determinants become INCREDIBLY comp...

14 days ago | 0

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vpa is not outputing enough digits
I think you may have a setting messed up on your computer. For example... X = sym(3)/32; vpa(X) ans = 0.09375 But now, if I...

14 days ago | 2

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change of expression ?
help solve help isolate Either will work. Why not try them? Best would be to read the documentation, the tutorials. You would ...

14 days ago | 0

Matlab and Fortran Precision Issue
No. In the most common case, such a disagreement is because you copied over some numbers from Fortran to MATLAB (or the other w...

14 days ago | 1

Starting Code from Middle
Why? Because you are not doing it correctly? What can I say? Maybe you are just running a really old version of MATLAB. Most lik...

15 days ago | 0

Difference between fittype 'poly1' and 'A*x+B'?
When you use the 'poly1' model, FIT is probably smart enough to understand this is a LINEAR model. And that it is solvable using...

15 days ago | 0

fitdist should be pdf^-1 but is seems not to return correctly
The problem is, you do not understand that evaluating the PDF is NOT the same thing as sampling random numbers from that distrib...

15 days ago | 0

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How to solve 4 non linear equations with 5 unknowns using least square method
You have an under-determined problem. If any solution exists, then there will be infinitely many solutions. (This is the case in...

15 days ago | 0

How to solve differential equations with varying constants
If a constant varies with time, then is it really a constant? Of course not. X=[ -47.9440 19.0518 -14.4223 -47.9833] If th...

15 days ago | 0

Need matrix or vector with 1,0,1,0,1,0.........
Hint: Use mod. For example, mod(1:25,2) But really, you need to start by looking at the Onramp tutorials, or read any text. I...

15 days ago | 0

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