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# Unexpected behavior with conditions in if loops....

## Unexpected behavior with conditions in if loops....

(OP)
Thanks in advance for looking at this; I have an .m file to finds the tangents to a given circle from any external points, and treats that circle like an obstruction so all the circle and points behind it are blocked. It works like this;

--M Code for a single circle obstruction--
format long
H = 1.75;
P = 100
g = 50;
f = 50;
gsize=100;

A = P/(2*pi*H);

%Basically, there's a tube emitting at the origin!

X = 0;
Y = 0;

%Tubecent is the distance from origin to centre circle
tubecent = sqrt((g/100. - X/1000)^2 + (f/100 - Y/1000)^2);

%the following angles are important
gamma = atan((g/100-X)/(f/100-Y))
theta = gamma - beta;
phi = gamma + beta;

for j = 1:1000
for k = 1:1000
r = sqrt( ((j/1000)-(X/100)).^2 + ((k/1000)-(Y/100)).^2 );
%r is the distance of the point in question to the tube
w = sqrt((g/100 - j/1000).^2 + (f/100 - k/1000).^2);
delta = tubecent-r;

ang = atan((j-X)./(k-Y)); %Angle between point and tube centre

if ang <= theta || ang >= phi
I = A ./ r;
elseif ang > theta && ang < phi
if w >= crad/100 && delta >= 0
I = A ./ r;
else
I = 0;

end
end

end
end
[XM,YM]=meshgrid(0.1:0.1:gsize , 0.1:0.1:gsize);

figure(3)
pcolor(XM,YM,log(Irad)), title('Log of Intensity versus distance graph')
xlabel('Centimetres'), ylabel('Centimetres')

--------------------------

This works fine, and running it in Matlab gives the expected result. Generalizing it to two circles shouldn't be much work, but however, I cannot get it to work; consider this..

--Potential M-File for 2 circular obstructions--

format long
H = 1.75;
P = 100

%circle co-ordinates (at centre)
g1 = 0.65;
f1 = 0.45;
g2 = 0.45
f2 = 0.65
gsize=100;

A = P/(2*pi*H);

%Basically, there's a tube emitting at the origin!

X = 0;
Y = 0;

%Tubecent is the distance from origin to centre circle
D1 = sqrt((g1 - X/1000)^2 + (f1 - Y/1000)^2);
D2 = sqrt((g2 - X/1000)^2 + (f2 - Y/1000)^2);

%the following angles are important-ish
gamma1 = atan((f1-X)/(g1 -Y))
theta1 = gamma1 - beta1
phi1 = gamma1 + beta1

gamma2 = atan((f2-X)/(g2-Y))
theta2 = gamma2 - beta2
phi2 = gamma2 + beta2

for j = 1:1000
for k = 1:1000
r = sqrt( ((j/1000)-(X)).^2 + ((k/1000)-(Y)).^2 );
%r is the distance of the (j,k) in question to the tube (x,y)
W1 = (sqrt((g1 - j/1000).^2 + (f1 - k/1000).^2)) - crad1/100;
W2 = (sqrt((g2 - j/1000).^2 + (f2 - k/1000).^2)) - crad2/100;
delta1 = D1 - r;
delta2 = D2 -r;

ang = atan((j/1000-X)./(k/1000-Y)); %Angle between point and tube centre

if ang <= theta1 || ang >= phi2 || ang > phi1 && ang < theta2 %tests of angle is less than theta
I = A ./ r;

elseif ang > theta1 && ang < phi1 && delta1 >= 0 && W1 >= 0
I = A ./ r;

elseif ang > theta2 && ang < phi2 && delta2 >= 0 && W2 >= 0
I = A ./ r;
else
I = 0;

end

end
end
[XM,YM]=meshgrid(0.1:0.1:gsize , 0.1:0.1:gsize);

figure(3)
pcolor(XM,YM,log(Irad)), title('Log of Intensity versus distance graph')
xlabel('Centimetres'), ylabel('Centimetres')

-----------------------------------------

This code doesn't quite work right; it seems to ignore the condition where the distance from the centre of the respective circles to the test point is less than the respective radius. Any ideas? I've been messing around with this for a week now and having no joy, regardless of what I do....

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