EDITED
You should call the function properly with input T like shown below:
T=[3 8] %example
Rblas4=arco(T) %function call
function RBlas4=arco(T) %function definition
p=51;
v=35;
n=50;
r=.08206;
spv=v/n;
Tca=150.87;
wa=1.002;
Tcc=304.2;
Pcc=72.9;
Pca=48.3;
wc=.225;
aa=.42747*((r*Tca)^2/Pca);
ac=.42747*((r*Tcc)^2/Pcc);
ba=.08664*((r*Tca)/Pca);
bc=.08664*((r*Tcc)/Pcc);
ma=.48508+1.55171*wa-.1561*(wa-1)^2;
mc=.48508+1.55171*wc-.1561*wc^2;
RBlas4=[(r*T(1))/(spv-ba)-aa*(1+ma*(1-sqrt(T(1)/Tca)))^2/(spv*(spv-ba))-p; %change this line too
(r*T(2))/(spv-bc)-ac*(1+mc*(1-sqrt(T(2)/Tcc)))^2/(spv*(spv-bc))-p];
end
Note: matlab is case sensitive Rblas4 should be RBlas4
