I am out of practice with MATLAB and I'm trying to get the sum from a loop to add itself to the sum of each iteration of the loop. I can accomplish by manually stepping the loop, but I know there must be an easier way. Can someone please help?

%Manual stepping of "loop"
clear
clc
h=input('What is height?  ');
l=input('What is length?  ');
w=input('What is frequency?  ');
y=input('How many iterations?  ');
x=0:0.001:l;
t=0;
F=(8*h)/(pi)^2;
n=1;
SUM=0
for n=1
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S4=F*(S1*S2*S3);
    SUM1=S4;
    figure
    plot(x,SUM1)
end
for n=n+1
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S5=F*(S1*S2*S3);
    SUM2=SUM1+S5
    figure
    plot(x,SUM2)
end
for n=n+1
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S6=F*(S1*S2*S3);
    SUM3=SUM2+S6
    figure
    plot(x,SUM3)
end
for n=n+1
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S7=F*(S1*S2*S3);
    SUM4=SUM3+S7
    figure
    plot(x,SUM4)
end
for n=n+1
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S8=F*(S1*S2*S3);
    SUM5=SUM4+S8
    figure
    plot(x,SUM5)
end
for n=n+1
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S9=F*(S1*S2*S3);
    SUM6=SUM5+S9
    figure
    plot(x,SUM6)
end
for n=n+1
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S10=F*(S1*S2*S3);
    SUM7=SUM6+S10
    figure
    plot(x,SUM7)
end

%What I thought might shorten code
clear
clc
h=input('What is height?  ');
l=input('What is length?  ');
w=input('What is frequency?  ');
y=input('How many iterations?  ');
x=0:0.001:l;
t=0;
F=(8*h)/(pi)^2;
n=1:y;
for n=1:y
    i=2*n-1;
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S4=F*(S1*S2*S3);
    SUM=sum(S4, i);
    figure
    plot(x,SUM)
end

Answer 1

[mbonus]

This is what it looks like you are trying to do to me

h=input('What is height?  ');
l=input('What is length?  ');
w=input('What is frequency?  ');
y=input('How many iterations?  ');
x=0:0.001:l;
t=0;%was this supposed to be a vector?
F=(8*h)/(pi)^2;
SUM = 0;
for n=1:y
    i=2*n-1;
  %%Update t here?
    S1=((-1)^((i-1)/2))/(i^2);
    S2=sin(i*pi*x/l);
    S3=cos(w*t);
    S4=F*(S1*S2*S3);
    SUM = SUM + S4;
    figure
    plot(x,SUM)
    title(['Plot of iteration ' num2str(i)])
end

Although you never modify t which will result in S3 always equaling 1, so maybe you meant to update t in the loop? Or did you mean to make t a vector like x?

[polkerface]

No, t is supposed to be zero in this instance for initial conditions...I just left it in there as a placeholder for future needs (in hindsight, I probably should have it as an input like the other things that might be variable for future runs).

Your code appears to be exactly what I need, will give it a try as soon as laptop finishes startup. I tried the

SUM=SUM+S4

on previous attempts and for some reason it kept returning the initial value for SUM (which is 0) plus the S4 value...I'll look back at old versions to see difference (that and the multiple plots were the reasons I went the painful route of manually stepping).

Okay, laptop and MATLAB are up...code works like I was trying to describe (changed the t to an input, and i in the string to n because i returns odd values rather than iterations). Still can't explain the SUM issue from my old version (always returning S4 value, maybe something I did wrong in trying symsum because it was that version).

Thank you so much for your help mbonus! And thank you too Image Analyst, apologies for not being more clear in my first post, but thanks for pointing that out to me.

[mbonus]

Glad to help. There have been a few times where I've had similar issues that you did with SUM, usually it goes down to using different capitalizations for the variable by mistake or maybe having an 's' at the end and then forgetting about it.

[Image Analyst]

I would not call the variable SUM. True, MATLAB is case sensitive so SUM is different than the built-in function named sum(), but still, it's better to not use the same name.

To be friendlier to the users, you might use a GUI to collect input numbers, like use inputdlg() instead of input(). Here's a code snippet/example that you can adapt:

% Ask user for two floating point numbers.
defaultValue = {'45.67', '78.91'};
titleBar = 'Enter a value';
userPrompt = {'Enter floating point number 1 : ', 'Enter floating point number 2: '};
caUserInput = inputdlg(userPrompt, titleBar, 1, defaultValue);
if isempty(caUserInput),return,end; % Bail out if they clicked Cancel.
% Convert to floating point from string.
usersValue1 = str2double(caUserInput{1})
usersValue2 = str2double(caUserInput{2})
% Check for a valid number.
if isnan(usersValue1)
    % They didn't enter a number.  
    % They clicked Cancel, or entered a character, symbols, or something else not allowed.
  % Convert the default from a string and stick that into usersValue1.
    usersValue1 = str2double(defaultValue{1});
    message = sprintf('I said it had to be a number.\nI will use %.2f and continue.', usersValue1);
    uiwait(warndlg(message));
end
% Do the same for usersValue2

Answer 2

[Image Analyst]

I have no idea what you really want to do. But this kind of syntax:

for n=n+1

while it may work, is nonsense. Please explain better what you're trying to do.

[polkerface]

Maybe that shows how out of practice I am.

for n=n+1

was the "manual stepping" of the loop (plus the copy-paste of everything else between that and its subsequent end).

To attempt to clarify (still working from the code that that little piece was pulled from), I would like to run F*S1*S2*S3, get its total, plot it, then run it again with a larger n (which translates to a larger odd i), add its total to the previous total, plot this new total, and on and on until the number of iterations (y) has been reached.

I thought symsum, sum, etc. would be better options, but I cannot wrap my head around how to accomplish the running tally of totals and multiple plots (don't mean subplot, I mean a plot per each new total). Is that more clear, or did I muddy it further?