Changing fraction to decimal form

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

Answer 1

[Star Strider]

Since your expressions contain symbolic variables, use the vpa function. (For those that are purely numeric, double will also work.)

[Rick]

How can I cut off the decimal after a few decimal points?

[Star Strider]

You can control the number of significant digits displayed with the second argument to vpa. It doesn’t offer the sort of floating point precision format options that (for instance) fprintf does.

[Rick]

Okay, thank you!

[Star Strider]

My pleasure!