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How do is code this last summation? I was able to do the first one but have no clue how to finish it?

Asked by Adam Schlei on 23 Mar 2019
Latest activity Commented on by Adam Schlei on 23 Mar 2019
Matlab question.GIF
function Senior_Project_code
%input values
y = 4;
n = 1;
L = 3;
x = 0:1:L;
E = 808/(y^2);
%c = atan(abs((x-a(2*i-1)))/y)*(180/3.14);
%s = (-0.0000000667*atan(abs((x-a(2*i-1)))/y)*(180/3.14).^4 ...
% + 0.0000157209*atan(abs((x-a(2*i-1)))/y)*(180/3.14).^3 ...
% - 0.0010081511*atan(abs((x-a(2*i-1)))/y)*(180/3.14).^2 ...
% + 0.0020817855*atan(abs((x-a(2*i-1)))/y)*(180/3.14) ...
% + 0.9991821678);
Axx(x+1) = 0;
for k = 1:n
Axx(x+1) = Axx(x+1) + E* ...
(-0.0000000667*(atan(abs((x-a*(2*k-1)))/y)*(180/3.14)).^4 ...
+ 0.0000157209*(atan(abs((x-a*(2*k-1)))/y)*(180/3.14)).^3 ...
- 0.0010081511*(atan(abs((x-a*(2*k-1)))/y)*(180/3.14)).^2 ...
+ 0.0020817855*(atan(abs((x-a*(2*k-1)))/y)*(180/3.14)) ...
+ 0.9991821678);
Ax = sum(Axx)/(L+1); %can I redo this to match my other equation?
display (Axx,'Brightness Values');
display (Ax,'Average Brightness');
Any help redoing Ax to match my above summation with i=1, to z-2... would be much appreciated.
Coding should be in for,if, then, and, or....type statements if possible.


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That code could be made more efficient by not rcalculating the atan four times, and you could use atand() instead of 180/3.14 . And you could almost certainly get some vectorization there, process all of the k values at the same time and sum() those.
But it is not clear what your question is about redoing to match another equation?
The statement about x=0,1,..L is deceptive, seeming to imply that x will be integer valued -- something that you rely on. But if you look at what is being passed into s as the first parameter ("x") it is L/16 (okay because L is 16 so L/16 gives the integer 1), and L/32 (not okay as that would give 1/2) and L-L/32 (which would give 16-1/2=15.5, not an integer).
Yes that is correct. I'm trying to code my MathCad formulas from the picture above. The problem I'm having is non-integer values. What I have in the picture is correct. The coding in Matlab is the problem I'm having. When I have non integer values I get array size errors. Is their ways around this, cause I originally had x = 0 : 0.1 : L so their were more test points being used, but the array sizes don't match then. And yes I do agree with all of what you saying (efficincy and rcalculating of atan four times), I'm not great at coding and any help for matching my MathCad program shown in the picture to the Matlab code would be great. Thanks a bunch.
In other words I need the matlab equation of Ax, to be this summation equation with z=17:Matlab question3.GIF
or if not possible I need the matlab equation of Ax, to be this summation equation with z=17:
Matlab question4.GIF
Any help would be great!!

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2 Answers

Answer by darova
on 23 Mar 2019
 Accepted Answer

Maybe a little bit clearer version:
y= 7.5, n=16, L=16 result: 118.22
y= 4, n=1, L=3 result: 46.31
function main
% input values
y = 4;
L = 3;
z = 17;
n = 1;
av = 0;
for i = 1:z-2
x = L/(z-1)*i;
av = av + s(x,y,n,L);
x = L/(2*z-2)*i;
av = av + s(x,y,n,L) + s(L-x,y,n,L);
av = av/z;
display('Average Brightness: '), av
function result = s(x,y,n,L)
% equations
E = 808.01/y^2.008;
a = L/(2*n);
c = @(i) atand( abs(x-a*[2*i-1])/y );
coeff = [
S = 0;
for i = 1:n
for j = 1:5
S = S + coeff(j)*c(i)^(5-j);
result = E*S;


found the error. when x = L/(2*z-2)*i get rid of the i and it comes out prefect!

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Answer by Walter Roberson
on 23 Mar 2019

%input values
y = 4;
n = 1;
L = 3;
z = 17;
c = @(x, y, n, l, i) atand(abs((x-l./(2.*n).*(2*i-1)))./y);
p = @(X) -0.0000000667*X.^4 + 0.0000157209*X.^3 - 0.0010081511*X.^2 + 0.0020817855*X + 0.9991821678;
s = @(x, y, n, l, c) sum(p(c(x(:), y, n, l, 1:n)),2);
zs = @(z, y, n, l, c) sum( s(l./(z-1).*(1:z-2), y, n, l, c), 1);
result = @(z, y, n, l, c) (zs(z, y, n, l, c) + s(l./(2*z-2), y, n, l, c) + s(l - l./(2*z-2), y, n, l, c)) ./ z;
result(z, y, n, L, c)
However the result is nowhere near 111


When y= 7.5, n=16, and L=16 the Average or Ax equation should equal Ax=111.99
When y= 4, n=1, and L=3 the Average or Ax equation should equal Ax=44.94
not sure why you say L=3 then use a lower case l in your equation. Doesn't this screw things up? Also where does big X come from? That should be the tangent function or what c equals. Doesn't the use of (i) in the equation mean imaginary? This is why I change i to k. Not sure if that is a thing, but I'm not sure what your doing here with no explanation. It would be one thing if it worked, but Nice try anyways though.
p = @(TEMPORARY_VARIABLE) -0.0000000667*TEMPORARY_VARIABLE.^4 + 0.0000157209*TEMPORARY_VARIABLE.^3 - 0.0010081511*TEMPORARY_VARIABLE.^2 + 0.0020817855*TEMPORARY_VARIABLE + 0.9991821678;
not sure why you say L=3 then use a lower case l in your equation. Doesn't this screw things up?
No. You need to learn about dummy parameters. For example
s = @(x, y, n, l, c) sum(p(c(x(:), y, n, l, 1:n)),2);
means the same thing as
s = @temporary_function_s;
function result = temporary_function_s(x, y, n, l, c)
p = evalin('caller', 'p');
result = sum(p(c(x(:), y, n, l, 1:n)),2);
which in turn means the same as
s = @temporary_function_s;
function result = temporary_function_s(First_Parameter, Second_Parameter, Third_Parameter, Fourth_Parameter, Fifth_Parameter)
p = evalin('caller', 'p');
result = sum(p(Fifth_Parameter(First_Parameter(:), Second_Parameter, Third_Parameter, Fourth_Parameter, 1:Third_Parameter)),2);
... almost. With some small details about exactly when p is imported into the function.
Thanks for the info, I will look into this. What value where you getting when y= 4, n=1, and L=3 @ z=17?

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