Unnecessary cast to dense matrix in fcm()

[dselivanov]

Tried to compare create_tcm() and fcm(). Got following:

Error in asMethod(object) :
Cholmod error 'problem too large' at file ../Core/cholmod_dense.c, line 105
9.asMethod(object)
8.as(x, "matrix")
7.as.matrix.Matrix(x)
6.as.matrix(x)
5.lower.tri(result, diag = FALSE)

This casts sparse matrix to dense (see source code for base::lower.tri() function):

    # discard the lower diagonal if tri == TRUE
    if (tri)
        result[lower.tri(result, diag = FALSE)] <- 0

Should be trivial to do it with Matrix functions and without casting to dense.

[kbenoit]

Thanks @dselivanov you're right on this. These are just pushed and need review, which I will be working on today.