Very simple simultaneous eqs.

I am working on a script to pinpoint acoustic sources from differences in arrival times. This is a very basic question but I'm new to Matlab so hopefully the answer will be very simple. This is what I have done so far.

function timediff

eq1 = '((D1^2-(t1^2)*(c^2))/(t1*c+D1*cos(y-theta1))*0.5)-x';

eq2 = '((D2^2-(t2^2)*(c^2))/(t2*c+D2*cos(theta3-y))*0.5)-x';

s=solve(eq1,eq2)

D1 = input('Enter value of D1: ');

D2 = input('Enter value of D2: ');

c = input('Enter value of speed of sound (c): ');

theta1 = input('Enter value of theta1: ');

theta3 = input('Enter value of theta3: ');

t1 = input('Enter value of time difference 1: ');

t2 = input('Enter value of time difference 2: ');

a=vpa(s.x)

b=vpa(s.y)

plot(a,b,'x')

When I run this and enter the paramaters it calculates a and b but doesn't evaluate them numerically - how do I do this because I would like to be able to plot them on a graph.

Many thanks in advance

Answer 1

[Sean de Wolski]

doc subs  %substitute numerical values
doc double  %convert symbolic to double precision

[jnaumann]

I tried using the double command and the following error message was produced;

??? Error using ==> mupadmex

Error in MuPAD command: DOUBLE cannot convert the input expression into a double array.

If the input expression contains a symbolic variable, use the VPA function instead.

Error in ==> sym.sym>sym.double at 936

Xstr = mupadmex('symobj::double', S.s, 0);

Error in ==> timediff at 12

a=double(s.x)

If I use the vpa command as suggested I still don't get the amsers in the numerical format.

Also how would i use the subs command because I have already entered the numerical values for the parameters?

[Sean de Wolski]

Use SUBS to substitute your values for D1 D2 c et al. into the s.x,s.y symbolics.