Why am i getting "Unable to perform assignment because the indices on the left side are not compatible with the size of the right side"

Question

Chidera Agu 2019-5-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/461276-why-am-i-getting-unable-to-perform-assignment-because-the-indices-on-the-left-side-are-not-compatib

回答： Raj 2019-5-10

function ydot=problem4data(W,X)
fa0=5; %mol/s
fb0=2*fa0;%mol/s
fi=2*fa0; %mol/s
ca0=2; %mol/dm^3
T1=325; %K
Ta=300; %K
T2=305;%K
Cpa= 20;%cal/molK
Cpb=Cpa;
Cpc=Cpa;
E=25; %kcal/mol
R=1.987*.001;%kcal/molK
Cpi=18; %cal/molK
Ua=320; %cal/s.m^3.K
Hrx= -20; %Kcal/mol
k2=.0002; %dm^6/kg.mol.s
alpha=.000115; %kg^-1
Cpsum=Cpa+Cpb+Cpi;
x=[0:0.1:1];%assumption
T=T1+((x.*(-Hrx))./(Cpsum));
Kc2=1000;
Kc1=Kc2.*exp((Hrx./R).*((1./T2)-(1./T)));
k1=k2.*exp((E./R).*((1./Ta)-(1./T)));
y1=1;%assumption
xenum=((3.*Kc1)./4)- sqrt(((3.*Kc1)./4)-((2.*Kc1).*((Kc1./4)-1)));%numerator xe equation
xedenom=2.*((Kc1./4)-1);%denominator xe equation
xe=xenum./xedenom;
pb= 1400; %kg/m^3
ra=-((k1.*ca0.*(T./T1).*y1).^2).*((1-x).*(2-x)-((4*x.^2)./Kc1));
rae=-((k1.*ca0.*(T./T1).*y1).^2).*((1-xe).*(2-xe)-((4*xe.^2)/Kc1));
Tnum=(Ua./pb).*(Ta-T)+(ra.*Hrx);
Tdenom=(fa0+fb0+fi).*(Cpsum);
ydot(1)=(-ra)./fa0;
ydot(2)=-rae./fa0;
ydot(3)=Tnum./Tdenom;
ydot(4)=(-alpha./(2.*y1)).*(T./T1);
ydot=ydot';
end

6 个评论
显示 4更早的评论隐藏 4更早的评论

KSSV 2019-5-10

What is W and X?? Inputs to the function.

Chidera Agu 2019-5-10

W ranges from 0 to 1000

X is what i just decided to use to represent x,xe,T,and y. (dx/dW, dT/dW, dy/dW)

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Raj 2019-5-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/461276-why-am-i-getting-unable-to-perform-assignment-because-the-indices-on-the-left-side-are-not-compatib#answer_374380

在 MATLAB Online 中打开

You must be getting error at line number 34 in your code. That's because your 'ra' is a 1x11 double type matrix which (after dividing by fa0) you are tying to assign to a single element of ydot. Again in the next line you are trying to assign 'rae' which is a 1x11 complex double type matrix to single element of ydot.

Try changing your code like this:

ydot(1,:)=(-ra)./fa0;
ydot(2,:)=-rae./fa0;
ydot(3,:)=Tnum./Tdenom;
ydot(4,:)=(-alpha./(2.*y1)).*(T./T1);

This will give you a ydot matrix of 11x4 complex double type matrix (after the transpose) in which your third and fourth columns will have repeated real values. you can extract the values out of ydot as per your requirement in the script where you are calling this function.