Solve Symsum equation for implied discount rate

Dear All,

I am trying to solve for a discount rate which sets the net present value to a specific value.

Stream = [-20000,  2000,  2500,  3500, -5000,  6500,...
          9500,  9500,  9500];
syms x k real;
eqn = symsum(Stream(1,k)*(1+x)^-k,k,1, length(Stream)) == 5274;
solx = solve(eqn,x)

Could anyone help to get the exact number for x?

Thanks in advance!

Answer 1

[Walter Roberson]

symsum() cannot be used for indexing. Create a vector of symbolic values and sum() that.

   eqn = sum(Stream .* (1+x).^-(1:length(Stream))) == 5274

[peterhack]

This did the trick. Additionally I have used vpasolve over a certain intervall to get the numeric value:

syms x k real;
eqn = sum(Stream .* (1+x).^-(1:length(Stream))) == 5274;
alpha = vpasolve(eqn,x,[0 1])