Extract Data from for loop
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I am attempting to plot SFC and TSFC vs The PRC values based on each value of Mach. I am trying to find a way to extract all calculated values of SFC and TSFC from the for loop for plotting. Any help would be appreciated
U = Mach*sqrt(gamman*R*Ta);
Toa = Ta.*((1+(((gammad-1)/2).*(Mach^2))));
To2 = Toa;
To2sTa = (1+((etad.*((To2./Ta)-1))));
Po2 = Pa.*((To2sTa).^(gammad/(gammad-1)));
for PRC = 5:5:100
Po3 = PRC.*Po2;
To3 = To2.*(1+((1./etac).*(PRC.^((gammac-1)/gammac))-1));
for To4 = [1500 1600 1700]
Cpb = ((R*gammab)/(gammab-1));
f = ((To3.*((To4./To3)-1))./((QR/Cpb)-To4));
Po4 = Po3;
To5 = To4-To3+To2;
Po5 = (Po4.*(1-(1./etat)*(1-(To5/To4))).^(gammat/(gammat-1)));
U7 = sqrt((2*etan*R*(gamman/(gamman-1)))*To5*((1-(Pa/Po5)).^(gamman-1/(gamman))));
SFC = ((1+f)*U7-U)/1000; %((kN*s)/(kg))
TSFC = f*SFC; %((kg)/(kN*s))
end
end
end
1 个评论
dpb
2014-10-21
Look at
doc meshgrid
for "the Matlab way" to evaluate a function over a rectangular grid
采纳的回答
Imran
2014-10-22
0 个投票
After
SFC = ((1+f)*U7-U)/1000; %((kN*s)/(kg));
Use
SFC = [[];SFC];
But define
SFC = [];
Before loop
Same for TSFC
1 个评论
SFC = [[];SFC];
This is the most inefficient way possible; "growing" the array by constant reallocation.
If not going to use the builtin facility of Matlab to evaluate over the 2D mesh via meshgrid at least preallocate the array...
Before the loop add...
N=length(5:5:100); % length of one dimension
SFC(N,3)=0; % array of Nx3 created automagically by reference
and initialize the row,column indices...
iP=0;
for PRC = 5:5:100
iP=iP+1; % increment outer (row)
...
iT=0; % initialize inner (column)
for To4 = [1500 1600 1700]
iT=iT+1; %
...
SFC(iP,iT) = ((1+f)*U7-U)/1000; %((kN*s)/(kg))
...
But again, see
doc meshgrid
and can eliminate loops entirely
更多回答（1 个）
Image Analyst
2014-10-21
0 个投票
You either have to add indexes to the variables so that you're not overwriting the same thing each time, or else you have to put the call to plot() inside the loop. Which way do you want to do it?
5 个评论
G
2014-10-21
Image Analyst
2014-10-22
I just returned to this now. It looks like you've accepted Imran's answer so I don't need to answer this. Good luck with that approach - though it's not what dpb and I would recommend.
dpb
2014-10-23
"You can lead a horse to water but..." :(
Image Analyst
2014-10-23
The weird thing is SFC = [[];SFC]; doesn't even do anything. [] is null so it's the same as SFC = [SFC]; which is the same as SFC=SFC, which does absolutely nothing. Oh well, whatever.
dpb
2014-10-23
Yeah, Imran intended to write
SFC=[];
for PRC = 5:5:100
...
for To4 = [1500 1600 1700]
...
SFC = [SFC;((1+f)*U7-U)/1000; %((kN*s)/(kg))];
...
I gave him a pass on that as he did say to initialize to null outside the loop that the following then was just a faux pas.
But the other thing bum about this solution besides the lousy performance is it's a 1D vector (of course, can fix that by reshape but as is it isn't particularly useful for OP's purpose and OP's experience level is likely such won't understand what result is where in the vector).
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