'ReturnConditions' creates error in 'solve'

Hi! I am trying to solve the following system of equations analytically. Matlab can't solve the general case (in which phi is not specified) so I set its value to -1.

syms i1 i2 gamma phi w r

firstfoc=( (2+r)*w/(1+r) ) * ...
    (gamma*i1^phi + (1-gamma)*i2^phi)^(1/phi)*gamma*i1^(phi-1)==1+r

secondfoc=((2+r)*w/(1+r) ) * ...
    (gamma*i1^phi + (1-gamma)*i2^phi)^(1/phi)*(1-gamma)*i2^(phi-1)==1

firstfoc=subs(firstfoc,phi,-1)
secondfoc=subs(firstfoc,phi,-1)

[i1sol, i2sol]=solve(firstfoc, secondfoc, i1, i2)

[i1sol, i2sol]=solve(firstfoc, secondfoc, i1, i2,'ReturnConditions',true)

As you can see, the first call to "solve" returns an answer, but warns that it's parameter-dependent and advises setting 'ReturnConditions' to true. However, doing so causes a rather opaque error. What's going on here, and is there an easy way to tell over what regions in the (gamma, w, r) parameter space there is a solution?

Any help would be greatly appreciated!

Answer 1

[Star Strider]

Provide output variables, and outputs to return the parameters and conditions:

syms i1 i2 gamma phi w r

firstfoc=( (2+r)*w/(1+r) ) * ...
    (gamma*i1^phi + (1-gamma)*i2^phi)^(1/phi)*gamma*i1^(phi-1)==1+r

firstfoc = 

secondfoc=((2+r)*w/(1+r) ) * ...
    (gamma*i1^phi + (1-gamma)*i2^phi)^(1/phi)*(1-gamma)*i2^(phi-1)==1

secondfoc = 

firstfoc=subs(firstfoc,phi,-1)

firstfoc = 

secondfoc=subs(firstfoc,phi,-1)

secondfoc = 

[i1sol, i2sol]=solve(firstfoc, secondfoc, i1, i2)

Warning: Solutions are only valid under certain conditions. To include parameters and conditions in the solution, specify the 'ReturnConditions' value as 'true'.

i1sol = 

i2sol = 

[isol1, isol2, parms, condx]=solve(firstfoc, secondfoc, [i1,i2], 'ReturnConditions',true)

isol1 = 

isol2 = 

parms = 

z

condx = 

.