# Changing fraction to decimal form

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Rick on 5 Oct 2015
Commented: Star Strider on 5 Oct 2015
Hello,
I am trying to change my fractions to numbers, but when I use the eval() function, it won't do it
V = 50; % cm^3
R = .05; % ohms
Vj = 30; % cm^3
DeltaH = 15000; % J/C
C = 4000; % K
cp = 2.7778e-4; % Wh/g K
cp_f = 9.7694e-4; % Wh/g K
U = 12.5e-4; % W/cm^2 K
A = 30; % cm^2
rho = 1.8; % g/cm^3
rho_f = 1.07; % g/cm^3
syms T Tj I Fj Tj_in
x = [Tj T];
u = [I Fj Tj_in];
y = x;
f1 = Fj/Vj*(Tj_in-Tj)+(U*A/(rho_f*cp_f*Vj))*(T-Tj);
f2 = I^2*R/(rho*cp*V)+I*DeltaH*exp(-C/(273+T))-(U*A/(rho*cp*V))*(T-Tj);
dx = [f1; f2];
A = jacobian(dx,x);
B = jacobian(dx,u);
C = jacobian(y,x);
D = jacobian(y,u);
Then here is my output
eval(A)
ans =
[ - Fj/30 - 2692700942717151/2251799813685248, 2692700942717151/2251799813685248]
[ 62500/41667, (60000000*I*exp(-4000/(T + 273)))/(T + 273)^2 - 62500/41667]
But I want these as numbers with decimals if possible! I wonder why eval() isn't working

Star Strider on 5 Oct 2015
Since your expressions contain symbolic variables, use the vpa function. (For those that are purely numeric, double will also work.)
Star Strider on 5 Oct 2015
My pleasure!