Empty sym: 0-by-1

When I run this code, my answer for A comes out as 'Empty sym: 0-by-1'

clc;clear;format compact;
syms V 
P=[0.98 1.97 4.93 9.86 49.36 98.69]; %atm
T=[573 573 573 573 573 573]; %K
R=461.5; %Pa*m3/mol*K
R=convpres(R,'Pa','atm');
R=R*1000; %L*atm/mol*K
GI=(P*V)-(R*T);
A=solve(GI,V)

A =
Empty sym: 0-by-1

Answer 1

[Torsten]

Use

A = double(arrayfun(@(i)solve(GI(i),V),1:numel(P)))

instead of

A = solve(GI,V)

[Dyuman Joshi]

which can be simplified to

out = double(arrayfun(@(x) solve(x,V), GI))

Answer 2

[Steven Lord]

Let's look at the equations you're trying to solve.

syms V 
P=[0.98 1.97 4.93 9.86 49.36 98.69]; %atm
T=[573 573 573 573 573 573]; %K
R=461.5; %Pa*m3/mol*K
R=convpres(R,'Pa','atm');
R=R*1000; %L*atm/mol*K
GI=(P*V)-(R*T)

GI = 

The first element of GI has a solution, as does the second element of GI. Is the solution for those two elements exactly the same? To ask that question another way, is there a value of V that satisfies all the elements in GI simultaneously?

A1=solve(GI(1), V)

A1 = 

A2 = solve(GI(2), V)

A2 = 

isAlways(A1 == A2)

ans = logical
   0

No, there isn't. So your original solve call that's looking for that one value of V that satisfies all the elements in GI simultaneously is correct to return an empty sym.

Now if you wanted a vector of values of V that satisfy each corresponding element in GI, that's possible to compute.

A = zeros(size(GI), 'sym');
for whichTerm = 1:numel(GI)
    A(whichTerm) = solve(GI(whichTerm), V);
end
A

A = 

Do they satisfy their equations?

result = zeros(size(GI), 'sym');
for whichEquation = 1:numel(GI)
result(whichEquation) = subs(GI(whichEquation), V, A(whichEquation));
end
result

result = 

Yes. Are they close to the same value?

vpa(A, 5)

ans = 

Nope. Not even same order of magnitude.

[Walter Roberson]

This is an important point: solve is always looking for simultaneous solution of all the inputs. It is designed for simultaneous equation solving, and does not have any option for solving each equation individually.