Extract Data from for loop

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G
G 2014-10-21
编辑： Walter Roberson 2016-1-15
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
dpb 2014-10-21
Look at
doc meshgrid
for "the Matlab way" to evaluate a function over a rectangular grid

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采纳的回答

Imran
Imran 2014-10-22
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
dpb
dpb 2014-10-22
编辑：dpb 2014-10-22
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

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更多回答（1 个）

Image Analyst
Image Analyst 2014-10-21
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
显示 3更早的评论
Image Analyst
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
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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