Very simple simultaneous eqs.

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jnaumann
jnaumann 2011-8-8
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

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回答（1 个）

Sean de Wolski
Sean de Wolski 2011-8-8
doc subs %substitute numerical values
doc double %convert symbolic to double precision
  2 个评论
jnaumann
jnaumann 2011-8-8
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
Sean de Wolski 2011-8-8
Use SUBS to substitute your values for D1 D2 c et al. into the s.x,s.y symbolics.

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