MATLAB: How to add two symbolic functions

differential equationssymbolic

The code below is to solve for differentiation symbolically; however, I cant add the qo1 and qo2. Any help is appreciated.
function []=Derivatives()
syms kLa RPM qsMax Sm Ki Ks Com V Xm Ko Yx qs qM mum qo qo1 YOSan YOSen dXmdt dComdt u
%%Given Relations
qs=symfun(qsMax*(Sm/(Ks+Sm+Sm*Sm/Ki))*(Com/(Ko+Com)),[qsMax Ks Sm Ki Ko Com]);
mum=symfun((qs-qM)*Yx,[qM Yx]);
qo1=symfun(((YOSan-YOSen)*mum*(0.96/0.375)),[YOSan YOSen]);
qo2=symfun(YOSen*qs,[YOSen]);
qo=plus(qo1,qo2);
%%Rates Symbolically
dXmdt=symfun(mum*Xm-(u/V)*Xm,[Xm u V Xm]);
dComdt=symfun(kLa*(Costar-Com)-qo*Xm-(u/V)*Com,[kLa Costar Com qo Xm u V ]);
diff(dXmdt,Xm)

Best Answer

qo = symfun(plus(qo1(YOsan, YOsen), qo2(YOsen)), [YOsan, YOsen]) ;
That is, invoke them with symbolic arguments to get a symbolic expression, add the expressions, and create a symbolic function from the results.
You will find that most of the time it is easier to work with symbolic expressions rather than symbolic functions.
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