Conversion to logical from sym is not possible.

my matlab code is the following:

clear 
syms rr
 g=3 
Fr1=(1.8-0.8.*(1+rr)./(1-7.56.*g*rr)) 
O1=0.01-0.11.*rr+0.06.*exp(23*rr)
 eff1=Fr1*rr/O1 
x=fminbnd(@(rr)-eff1,-1,1) 

after executing this code ,it shows error message:

eff1 = (rr*(((4*rr)/5 + 4/5)/((567*rr)/25 - 1) + 9/5))/((3*exp(23*rr))/50 - (11*rr)/100 + 1/100)

Conversion to logical from sym is not possible.

Error in fminbnd (line 336) if fu <= fx Error in e2 (line 9)

x=fminbnd(@(rr)-eff1,-1,1)

how can i solve this problem?thank a lot!

Answer 1

[Sargondjani]

g = 3;

eff1=@(rr)-(1.8-0.8.*(1+rr)./(1-7.56.*g*rr))*rr/(0.01-0.11.*rr+0.06.*exp(23*rr));

x=fminbnd(eff1,-1,1);

You could still define your subfunctions separtately, but this will give you an anwer. You dont need the symbolic stuff.

[Hopejiun Jo]

thanks.

in the subfunction,i can use min() to find the minimum.however,if i still want to use fminbnd() to find the minimum,what is the cause of mistake?

[Walter Roberson]

@Hopejiun Jo

Are you asking why your symbolic solution failed? If so then it is because @(rr)-eff1 does not evaluate -eff1 with respect to rr at all, and instead just returns whatever value it had before, namely the symbolic expression; furthermore fminbnd is not designed to work with symbolic outputs.

You would need

x=fminbnd(matlabFuncton(-eff1),-1,1) 

[Hopejiun Jo]

thanks.it can work!