# How to use solve function in matlab in this case

1. Oct 26, 2007

### oahsen

We are trying to find the roots of a function where exp(f(z)) = c. (where c is a complex number). Also f(z) is a polynomial function. The function will have the following format:
expsolve( [an an-1 …] , c ) where n is the degree of “z”.
For do this I took the natural logarithm of both sides and find f(z) = log(c). The code I have written so far is as follows;

function expsolve(v,c);
len=length(v)
temp=log(c);
syms z;
syms def;
syms first;
first=0;
for(a=1:len)
def=v(len-a+1)*(z^(a-1))
first=first+def
end
first
equ=first-log(c)

--------------------
now if I write expsolve([1 5 3], 4) for instance
until the first part it gives me the correct result (first=z^2+5*z+3)
however, I could not do the rest. how can I find the roots of first-log(c).

I tried to write different combination of :
solve('equ=0','z').
However, it gave my either an error or a illogical answer.

How can I proceed in this question. Besides the code I have written is there any simpler way to solve the question?