# How to construct matrix for variable radius?

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I G il 10 Gen 2019
Risposto: Eugenio Grabovic il 29 Gen 2019
I have divergent geometry, where my longitudinal coordinate is:
z=1:-0.001:0;
Wall of the pipe is defined with this law:
ri=0.7;
R=ri-z*(ri-1);
and ri is inlet radius of the pipe (when z=0), outlet radius is 1 (it means when z=1).
I need to define radius, which will be transverzal coordinate r, it need to go from -R(z) to R(z) for one value of z, but I need to have all values of z. It means that R is not constant, and it is possible to have different number of points at different values of z. Is it possible so solve this for the same number of points in every cross section, and to have r as matrix? Or is it possible to solve it with different number of points in every cross section?
Later I need to calculate D, will D also be matrix?
D=r.*r-R(z).*R(z)ma
I have tried this, and all does not work:
r=[0:R];
r=[0:R(:,0);
0:R(:,1)];...
r=-R:R;
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Jan il 11 Gen 2019
I do not understand the question. "All does not work" is not a clear description of the problem. I cannot guess, what you want to achieve and if you get an error message, it would be efficient, if you post it here.
What does this mean: "It means that R is not constant, and it is possible to have different number of points at different values of z"? What is not constant - the contents or the dimensions?

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### Risposte (1)

Eugenio Grabovic il 29 Gen 2019
I maybe understood what you're asking for:
k = 100; % number of transversal discretization
ri = 0:0.7/k:0.7;
i = 0;
for z=1:-0.001:0;
i = i + 1;
R(i,:) = ri-z*(ri-1); % storing the radius values in rows (each row is computed for a different z)
end
About the "D" computation i don't know what "ma" is, sorry.
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