Raising a matrix to a power

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Nathan Stawasz
Nathan Stawasz 2019-9-7
评论： Walter Roberson 2019-9-10
I want to raise the Tr value to the power of 1/2. I keep getting the same error. Screen Shot 2019-09-07 at 6.53.10 PM.png

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回答（2 个）

Guillaume
Guillaume 2019-9-7
The problem is not the .^0.5, it's the ^2, which probably should be .^2. Note that x.^0.5 is the same as sqrt(x).
However, If Tr is a matrix, then it's unlikely that alpha(Tr) is a valid target for assignment.
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madhan ravi
madhan ravi 2019-9-9
Also note don’t name variable in the name of MATLAB’s inbuilt function. alpha() is an inbuilt function.
Guillaume
Guillaume 2019-9-9
Yes, as said, the current error is trivially fixed by replacing ^2 by .^2. As for the alpha(Tr) =, it's not clear what you intended to do with that.

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Bruno Luong
Bruno Luong 2019-9-9
% This script will generate a plot of pressure P (in bar) as a function of molar
% volume V (in cm^3/mol) for various values of temperature T (in K) for
% ethylene as described by the Peng-Robinso n equation of state.
T=[260;270;280;282.4;290;300;310];
V=[50:400];
R= 83.14; % cm^3bar/mol K
Tc= 282.4; %K
Tr= T./Tc;
a= 5.001*10^6;% barcm^6/mol^2
b= 36.24; % cm^3/mol
k= 0.5098;
alpha = (1+k*(1-((Tr).^0.5)).^2);
P= (((R*T)./(V-b))- (a*alpha)./((V.^2)+((2*b*V)-b.^2 ))) ;
surf(V,alpha,P)
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madhan ravi
madhan ravi 2019-9-10
编辑：madhan ravi 2019-9-10
The comment wasn’t meant to you , it was meant for the OP who reads it, if you took it that way then I apologise. As I said earlier it is not a problem for you but for others it might.

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