Warning: Explicit solution could not be found.

Hallo,

I have been trying to to generate a 100x100 table that includes the solution of a certain equation for 10000 different inputs.

My m.file has a double counter i and j and loops as follows

clear
clc

W=zeros(100,100);

for i=1:100
    for j=1:100
        W(i,j)=double(cost_factor(i/100,j/100,2));
    end
end

The function cost factor is called at every iteration and its source code is provided bellow:

function [w] = cost_factor(b,b_plus,x )
%This function is a subroutine that computes the cost factor w as a function of b,b_dash,x

% Inputs

% b        previous day's portfolio 
% b_plus   this day's portfolio
% x        previous day's stock price relative (x=2 or x=0.5)

% Outputs

% w        present cost relative 

c_p=0.01;
r=0;
syms w
assume(1/(1+c_p)<=w<=1)

w=solve(w+0.5*c_p*(abs(b_plus*w-b*x/(b*x+(1-b)*exp(r)))+(b_plus*w-b*x/(b*x+(1-b)*exp(r))))+...
    0.5*c_p*abs((1-b_plus)*w-(1-b)*exp(r)/(b*x+(1-b)*exp(r))+(1-b_plus)*w-(1-b)*exp(r)/(b*x+(1-b)*exp(r)))==1,w);

end

Everything seems to work fine when the first argument cost factor's inputs is larger than the second but in some of the cases where the converse is true I get the message 'Warning: Explicit solution could not be found. '. More specifically, I get this message when the difference b_plus-b>=0.48. So, my loop stops at W(1,52). Finally, note that b and b_plus are assigned values in [0,1] by the counters. Anyone that could enlighten me on the issue?

Thanks in advance,

Konstantinos

[Walter Roberson]

At the command prompt, please command

dbstop if warning

and then run your code. When it stops in the debugger, please use dbstep until you get back to the cost_factor routine. Then, please show us the expression

w+0.5*c_p*(abs(b_plus*w-b*x/(b*x+(1-b)*exp(r)))+(b_plus*w-b*x/(b*x+(1-b)*exp(r))))+...
  0.5*c_p*abs((1-b_plus)*w-(1-b)*exp(r)/(b*x+(1-b)*exp(r))+(1-b_plus)*w-(1-b)*exp(r)/(b*x+(1-b)*exp(r)))

Caution: it is safer to write out that compound assumption in full,

assume(1/(1+c_p)<=w & w <= 1)