Hi Julians, I've developed a Julia package to manipulate symbolic linear expressions with both scalar and matrix coefficients: https://github.com/cdsousa/LinearExpressions.jl
I created it mainly to manipulate large linear matrix inequalities (LMI<http://en.wikipedia.org/wiki/Linear_matrix_inequality>) for SDP optimization. Two notes: the tests are not extensive; the main LinExpr type is not immutable, although from a mathematical pov it may make more sense to be. Cristóvão D. Sousa
