Multiple outputs from a for loop

Basic problem, but I can't find the solution:

consider basic a for loop:

for i = 1:5
    z(i)=3*i
end

It produces a vector z= [3 6 9 12 15]. What I need is all the components of the vector z as a sperate variables(scalars), let,s say

z1=3, z2=6 and so on. How can I do that?

Thanks in advance

Roger Kalvig

[Stephen23]

"What I need is all the components of the vector z as a sperate variables(scalars)"

Why?

What do you imagine that you can do with lots of scalars, that is not possible using indexing?

"say z1=3, z2=6 and so on."

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

[KSSV]

Already you have that in hand.

z(1), z(2),...z(n) etc.,

[Roger Kalvig]

Ok seems I need to describe my entire problem instead of decomposing it into pieces.

The goal is to perform numerical integracion of two functions. One of them is my function fcn looking like this:

function y = fcn(x)

Bext = 0.6;

G = 10.553;

if x < 0

y = 0;

elseif x == 0

y = 100;

elseif x == 180

y = 100;

elseif x > 180

y = 0;

else

y = 1./(G.*Bext.*(sind(x)));

end

end

which is simple relationship defined for 3 ranges and 2 x points.

The second function is Gaussian function:

function y = myGausstest(x)

A = 10;

w = 20;

xc = 90;

y = A.*exp(-0.5*((x-xc)./w).^2);

end

Now fcn is always constant, but Gauss is moving along x axis. All parameters of Gauss function remain constat except xc. So my idea was to create a for loop:

for xc = -100:10:280 (some range suiting fcn function)

"do integration here of the product of both functions fcn*myGausstest for integral limts (xc-d,xc+d)" using trapz or integral

end

Finally I need do plot the result

plot(x, result of integration)

Any help is appreciated.

Roger Kalvig

[Stephen23]

https://xyproblem.info/

https://en.wikipedia.org/wiki/XY_problem

https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem

Answer 1

[Stephen23]

Rather than distracting with anti-pattern numbered variables (like you asked about), instead you should just use basic, normal, efficient, easy, simple, standard indexing. Indexing is how MATLAB works best.

d = 5;
xc = -100:10:280; % (some range suiting fcn function)
iv = nan(1,numel(xc));
fh = @(x) fcn(x) .* myGausstest(x);
for k = 1:numel(xc)
    % do integration here of the product of both functions fcn*myGausstest for integral limts (xc-d,xc+d)" using trapz or integral
    iv(k) = integral(fh,xc(k)-d,xc(k)+d);
end

Warning: Reached the limit on the maximum number of intervals in use. Approximate bound on error is 6.7e-03. The integral may not exist, or it may be difficult to approximate numerically to the requested accuracy.

Warning: Minimum step size reached near x = 180. There may be a singularity, or the tolerances may be too tight for this problem.

plot(xc,iv)

function y = fcn(x)
Bext = 0.6;
G = 10.553;
y = 1./(G.*Bext.*sind(x));
y(x<0) = 0;
y(x==0) = 100;
y(x==180) = 100;
y(x>180) = 0;
end
function y = myGausstest(x)
A = 10;
w = 20;
xc = 90;
y = A.*exp(-0.5*((x-xc)./w).^2);
end

[Roger Kalvig]

One problem i can see is I already defined xc within

function y = myGausstest(x)

A = 10;

w = 20;

xc = 90;

y = A.*exp(-0.5*((x-xc)./w).^2);

end

so idea is to express Gauss in fh explicitely:

fh = @(x) fcn(x) .* A.*exp(-0.5*((x-xc)./w).^2);

but again, matrix dimensions are incorrect.

[Stephen23]

"One problem i can see is I already defined xc within"

Presumably you only intend the xc inside the function to refer to a single value, not the entire vector, in which case you can easily pass the value by parameterizing the function:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

For example:

d = 5;
xc = -100:10:280; % (some range suiting fcn function)
iv = nan(1,numel(xc));
for k = 1:numel(xc)
    fh = @(x) fcn(x) .* myGausstest(x,xc(k)); % parameterize function
    iv(k) = integral(fh,xc(k)-d,xc(k)+d);
end

Warning: Reached the limit on the maximum number of intervals in use. Approximate bound on error is 1.7e+02. The integral may not exist, or it may be difficult to approximate numerically to the requested accuracy.

Warning: Minimum step size reached near x = 180. There may be a singularity, or the tolerances may be too tight for this problem.

plot(xc,iv)

function y = fcn(x)
Bext = 0.6;
G = 10.553;
y = 1./(G.*Bext.*sind(x));
y(x<0) = 0;
y(x==0) = 100;
y(x==180) = 100;
y(x>180) = 0;
end
function y = myGausstest(x,xc)
A = 10;
w = 20;
y = A.*exp(-0.5*((x-xc)./w).^2);
end

[Roger Kalvig]

Thanks very much for help