How to run a for loop with two functions (nested for loop?)
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I am trying to perform a series of iterative calculations given two inputs. First I want to calculate for three pressures. Second, I want to calculate over a range of values from 0:0.01:1.0. I am using two functions: one from the XSteam.m package and one user-defined function. I am getting an error with the second function but I don't really know how to resolve this. First is the input in the script.
P = [50.0, 100.0, 150.0]; % Pressure (bars)
alpha = 0.0:0.01:1.0; % Void fraction from 0 to 1 in increments of 0.01
dh = 0.01; % Pipe diameter in meters (1 cm = 0.01 m)
for i = 1:numel(P);
sigma(i) = XSteam('st_p',P(i));
rhof(i) = XSteam('rhoL_P',P(i));
rhov(i) = XSteam('rhoV_P',P(i));
for n = 1:numel(alpha);
a(n) = calc_a( alpha, sigma(i), rhof(i), rhov(i), dh );
end
end
The values with XSteam are correctly generated if I put them in their own loop but I am unable to get the second function working when running through a for loop. Here is the calc_a function
function [ a ] = calc_a( alpha, sigma, rhof, rhov, dh )
g = 9.81;
db = sqrt(sigma /(g*(rhof - rhov)));
if alpha < 0.5
a = (6*alpha)/ db
elseif alpha >0.8
a = (4*sqrt(alpha))/ dh
else
omega = (alpha - 0.5)/(0.8 - 0.5)
a = ((6*alpha)/ db)*(1-omega) + ((4*alpha)/ dh)*omega
end
end
Is there a better way to do this or what am I missing? Thanks for the help.
1 个评论
SALAH ALRABEEI
2021-6-5
I think u might have a mistake in alpha in the 2nd loop. If Iam correct you should send one value of apha at foe each iteration. So it is alpha(i) not alpha
采纳的回答
Pretty sure that you're just intending to process alpha one element at a time, so just do that. Of course, you're overwriting a each time the outer loop cycles, so you'll want to fix that too.
P = [50.0, 100.0, 150.0]; % Pressure (bars)
alpha = 0.0:0.01:1.0; % Void fraction from 0 to 1 in increments of 0.01
dh = 0.01; % Pipe diameter in meters (1 cm = 0.01 m)
for m = 1:numel(P)
sigma(m) = XSteam('st_p',P(m));
rhof(m) = XSteam('rhoL_P',P(m));
rhov(m) = XSteam('rhoV_P',P(m));
for n = 1:numel(alpha)
a(m,n) = calc_a( alpha(n), sigma(m), rhof(m), rhov(m), dh );
end
end
% user-defined function is unchanged
The output is now a matrix, with one row for each value of P. If you leverage implicit array expansion available since R2016b, you can avoid the inner loop.
P = [50.0, 100.0, 150.0]; % Pressure (bars)
alpha = 0.0:0.01:1.0; % Void fraction from 0 to 1 in increments of 0.01
dh = 0.01; % Pipe diameter in meters (1 cm = 0.01 m)
M = numel(P);
sigma = zeros(M,1);
rhof = zeros(M,1);
rhov = zeros(M,1);
for m = 1:M
% i guess xsteam doesn't handle vector inputs
sigma(m) = XSteam('st_p',P(m));
rhof(m) = XSteam('rhoL_P',P(m));
rhov(m) = XSteam('rhoV_P',P(m));
end
% this is everything that the calc_a() used to do
% but now it's vectorized
g = 9.81;
db = sqrt(sigma ./(g*(rhof - rhov)));
omega = (alpha - 0.5)/(0.8 - 0.5);
m1 = alpha<0.5;
m2 = alpha>0.8;
% this should be identical to a
A = ((6*alpha)./ db).*m1 + ((4*sqrt(alpha))/ dh).*m2 ...
+ (((6*alpha)./ db).*(1-omega) + ((4*alpha)/ dh).*omega).*(~m1 & ~m2);
Whichever method you use is up to you.
2 个评论
Kevin Burg
2021-6-5
DGM
2021-6-5
All that's really necessary for the second method to work is that sigma, etc be oriented orthogonal to alpha. Then when elementwise arithmetic is performed on them, the result is a matrix. The legacy way of doing the same is to use bsxfun().
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