# Writing mathematical expression in a file

I am trying to write a mathematical expression as `variable = expression` in the output file.

The current method that I am doing is through `WriteString` as

``expr = -((a*b*y^2*(-1 + z)*z*(1 + a*b + z))/(1 + a*b)^2) +         (z*(1 + a*b - a*b*z + (z + a*b*z)^2))/(1 + a*b)^2 -         (y*z*((-1 + z)^2 + a*b*(2 - 3*z + z^2) + a^2*b^2*(1 - z + z^2)))/(1 + a*b)^2 expression = CForm[expr] /. {Power->pow}; (*expression = CForm[HornerForm[expr]] /. {Power->pow};*) str=OpenWrite["output.hh"]; WriteString[str," double variable = ", expression,";"]; (*WriteString[str," double variable = ", ExportString[expression,"Text"]];*) Close[str]; ``

The output is

`` cat output.hh  double variable = -(a*b*(-1 + z)*z*(1 + a*b + z)*pow(1 + a*b,-2)*pow(y,2)) - y*z*pow(1 + a*b,-2)*(pow(-1 + z,2) + a*b*(2 - 3*z + pow(z,2)) + pow(a,2)*pow(b,2)*(1 - z + pow(z,2))) + z*pow(1 + a*b,-2)*(1 + a*b - a*b*z + pow(z + a*b*z,2)); ``

I want to break the line as the original `expr` (or after some user-specified column say 80) i.e.

`` double variable = -(a*b*(-1 + z)*z*(1 + a*b + z)*pow(1 + a*b,-2)*pow(y,2)) -                    y*z*pow(1 + a*b,-2)*(pow(-1 + z,2) + a*b*(2 - 3*z + pow(z,2)) + pow(a,2)*pow(b,2)*(1 - z + pow(z,2))) +                     z*pow(1 + a*b,-2)*(1 + a*b - a*b*z + pow(z + a*b*z,2)); ``

Although this might not lead to optimized expression for numerical evaluation, however it is wanted as beautification. Also how should one optimize expression for further processing to other languages. Any suggestion? `Experimental`OptimizeExpression` and `HornerForm` are some options. Any other recommendation? `MathCode` is much costly ðŸ˜€