Find the exponent of a variable in a symbolic expression

I have a symbolic expression lets say:

e=sym('g*e/w*N');

How can i find the exponent of N (in this case it's 1). Exponent can vary from -10 to 0 to 10.

thanks in advance

Answer 1

[Walter Roberson]

Please be cautious about using the same name ('e') for the expression variable and inside the expression. You will run into problems if you use subs().

Anyhow, please see coeff()

[Tamás Király]

Thanks for the coeff() tip. It led me to the solution.

Just in case, maybe anyone will be interested in the future:

expression = sym('t*r*g/N/r');

variable = sym('N');

[num den] = numden(expression);

[~, b]=coeffs(num,variable);

[~, d]=coeffs(den,variable);

temp = [simple(evalin(symengine,['log(' char(b) ')/log(' char(variable) ')']));

simple(evalin(symengine,['log(' char(d) ')/log(' char(variable) ')']))];

r = temp(1) - temp(2);

'r' equals the exponent value of variable 'N'

[Walter Roberson]

I believe you should be able to skip the evalin's:

temp = simplify(log(b) / log(variable));

temp2 = simplify(log(d) / log(variable));

I noticed that you repeat r in your expression in such a way that the r cancel out. Was that intended?

Your formula will fail (partly because your requirements are not well defined) if either the numerator or denominator (or both) are polynomials in the variable.

My reference to coeff() rather than coeffs() was correct: see http://www.mathworks.com/help/toolbox/mupad/stdlib/coeff.html

But even easier would be to use

expression = sym('t*r*g/N/r');

variable = sym('N');

r = double(feval(symengine,'degree', numer(expression), N) - feval(symengine, 'degree', denom(expression), N));

You _might_ even be able to use

expression = sym('t*r*g/N/r');

variable = sym('N');

r = double(feval(symengine,'degree', expression, N));