MATLAB - The Language of Technical Computing

[foilman8805]

Love it or hate it, it's a high level computing language and an excellent analysis tool. I know we have some aspiring engineers in college who either are, or are soon to be immersed in this program and will be looking for help. The learning curve is extremely high, especially if you have no prior experience with programming. In this thread, you can post your code, ask for help from those of us who are more experienced, show people cool things they never knew about MATLAB, "code golf" or simply just show off.

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[tangomango]

Re: MATLAB - The Language of Technical Computing

Wow haven't posted in ages...

Does anyone know of a good site that gives tutorials on MATLAB? I'm struggling with it in my engineering class.

[woker-X]

Re: MATLAB - The Language of Technical Computing

what are you doing with it??

you can search for matlab exchange on google to get some programs similar to what you are doing.

EDIT: http://www.mathworks.com/matlabcentral/fileexchange/

[foilman8805]

Re: MATLAB - The Language of Technical Computing

tango, what kind of help are you looking for?

[tangomango]

Re: MATLAB - The Language of Technical Computing

We learned for-loops, if-or statements, array manipulations and more. I mainly don't understand for-loops. For instance, I was given a 5D array with length of 10 10 20 10 10, and told to use nested for-loops to find the maximum number in the array.

Do you have any advice on how to learn programming more efficiently? This is my first programming class and I'm having a rough time haha.

Example of a problem: Write a loop that finds the number under 1000 with the greatest number of
unique prime factors. (Since many numbers under 1000 have the same `greatest'
number of unique prime factors, find only the FIRST number that meets this
criterion.)

I had

for vector = 1:10
    factors(vector) = length(unique(factor(vector))); %Creates vector of the lengths of unique prime factors
    
end

After that I don't know how to find the first largest number from that vector.

[foilman8805]

Re: MATLAB - The Language of Technical Computing

The only advice is to program, program and program more. Occasionally seek help from people who know more than you. That's really it. You have to immerse yourself in order to get better. Practice makes perfect, etc.

And for a beginning programming class, I'm hoping what you really meant was you have a 1D array with 5 elements (length of 5). MATLAB doesn't handle 5D arrays lol.

[tangomango]

Re: MATLAB - The Language of Technical Computing

To clarify the 5D problem, I was given temperature data from 5 variables (x,y,z,t,s). I'd like to clarify more but it was a quiz problem and I don't really remember the specifics.

[foilman8805]

Re: MATLAB - The Language of Technical Computing

We learned for-loops, if-or statements, array manipulations and more. I mainly don't understand for-loops. For instance, I was given a 5D array with length of 10 10 20 10 10, and told to use nested for-loops to find the maximum number in the array.

Do you have any advice on how to learn programming more efficiently? This is my first programming class and I'm having a rough time haha.

Example of a problem: Write a loop that finds the number under 1000 with the greatest number of
unique prime factors. (Since many numbers under 1000 have the same `greatest'
number of unique prime factors, find only the FIRST number that meets this
criterion.)

I had

for vector = 1:10
    factors(vector) = length(unique(factor(vector))); %Creates vector of the lengths of unique prime factors
    
end

After that I don't know how to find the first largest number from that vector.

Use the "max" function to the find the largest number in an array, i.e.:

max(factors) will return the maximum number in the array you named factors in your for loop.

[tangomango]

Re: MATLAB - The Language of Technical Computing

The problem I'm having is that when I try to find the location of the maximum value from 'factors', it does not seem to work. Instead of a displaying '6' as I would like it to, it gives me 1.

 for vector = 6:10
    factors(vector) = length(unique(factor(vector))); %Creates vector of the lengths of unique prime factors
    a = find(max(factors));
end
disp(a)

Thanks for the help by the way.

[foilman8805]

Re: MATLAB - The Language of Technical Computing

If you want to find the location:

[a,b] = find(max(factors)); will return the index value of the largest number in the array by row and column, respectively.

Then you'd want to do:

disp(factors(a,b))

[foilman8805]

Re: MATLAB - The Language of Technical Computing

Write a loop that finds the number under 1000 with the greatest number of unique prime factors. (Since many numbers under 1000 have the same `greatest' number of unique prime factors, find only the FIRST number that meets this criterion.)

for i = 1:999
   x(i) = length(unique(factor(i)));
end

y = ind2sub(size(x),find(x==max(x)));
answer = min(y);

disp('The answer is:')
disp(answer)

One of many ways to do this. I didn't include everything in the loop though, so maybe I violated the rules. Whatever.

[tangomango]

Re: MATLAB - The Language of Technical Computing

I'm a little confused at this part:

 y = ind2sub(size(x),find(x==max(x)));
answer = min(y);

What does ind2sub do? Does it take all of the max values of x into a vector?

[foilman8805]

Re: MATLAB - The Language of Technical Computing

Dude, when you see something in MATLAB you don't immediately know and you want to know what it does you should consult the help files.

Type in the command window "help ind2sub". It'll provide a much better explanation than I can give.