find coefficients in an equation
[coef]=findcoef(str,car)
str = the equation analyzed
car = the default car for the beginning of the coefficients
coef = the names of the coefficients
findcoef('a1+a2*x1+(a3-a2)*x2+(a4-a3)*a5b','a') //returns ['a1';'a2';'a3';'a4']. The main usage is in econometric functions where the user must give the text of an equation (nls, twosls, threesls,…).