Error regarding "unknown variable"

I am trying to do an integration of the following problem: "Use MATLAB to write a script to determine work (w) during reversible isothermal expansion (T = 295K) from Vm(i) = 11.2 L/mol to Vm(f) = 33.6L/mol: (a) perfect gas"

When I type in the following code:

%int of p with respect to Vm ideal

clear 

clc

syms R T Vm; %ideal gas 

assume (T>0 Vm>0) %restrictions of T and Vm

p=R*T/Vm; %ideal gas law

f=in(p,Vm); %int of p wrt Vm

g=in(p,Vm,11.2,33.6); %int of p wrt Vm from 11.2L/mol to 33.6 L/mol

h=subs(g,[R,T],[0.0821,295]); %R=0.0821 atmL/Kmol T=295K

r=double(h); %final value

I am getting an error in the 5th line saying that Vm is an unknown variable. If i delete Vm I get the following error:

'integer', 'rational', 'real', 'positive'

The input did not match any of the valid strings.

Error in sym/in (line 11)
mset = setToMuPADSet(set);

Error in set3p1a (line 7)
f=in(p,Vm); %int of p wrt Vm

Caused by:
Error using validatestring>checkString (line 86)
Expected input to be one of these types:
char
Instead its type was sym.

I was how to correct this error and why matlab is not recognizing Vm as a variable even though i put it in the syms line.

[Guillaume]

Rather than putting blank lines between each line of code. Just paste your code as is, then click on the {}Code button at the top of the edit box.

Answer 1

[Walter Roberson]

assume (T>0 & Vm>0) %restrictions of T and Vm

f = int(p,Vm); %int of p wrt Vm

You were using "in" rather than "int"