problem using solve

Trying to find equilibrium solutions for a simple ODE system using matlab 7.10. The following commands were entered (commands based on earlier versions of matlab) with errors messages included:

dn1 = 'r*n1*(k-n1)/k-c*(1-exp(-a*n1/c))*n2'

dn2 = 'b*c*(1-exp(-a*n1/c))*n2-d*n2'

[n1hat,n2hat] = solve(dn1,dn2,'n1,n2') ??? Error using ==> mupadmex Error in MuPAD command: Division by zero [_power]; during evaluation of 'ff'

Error in ==> sym.sym>sym.mupadmexnout at 2003 out = mupadmex(fcn,args{:});

Error in ==> solve at 76 [symvars,R] = mupadmexnout('mllib::solvefull',eqns,vars);

Any suggestions?

Answer 1

[Walter Roberson]

Try

[n1hat,n2hat] = solve(dn1,dn2,'n1', 'n2')

with the two variables to solve for separated.

[michael golinski]

nope, still get the same error message:

Error using ==> mupadmex

Error in MuPAD command: Division by zero [_power];

during evaluation of 'ff'

Error in ==> sym.sym>sym.mupadmexnout at 2003

out = mupadmex(fcn,args{:});

Error in ==> solve at 76

[symvars,R] = mupadmexnout('mllib::solvefull',eqns,vars);

[Walter Roberson]

I don't know. This appears to be something specific to MuPAD, and possibly even to the MuPAD version. The solution set is:

n1 = 0, n2 = 0

n1 = k, n2 = 0

n1 = -ln((b*c-d)/(b*c))*c/a, n2 = -r*ln((b*c-d)/(b*c))*c*b*(k*a+ln((b*c-d)/(b*c))*c)/(k*d*a^2)