Dear Hans,

Here is the file in my desktop.
The reason I didn¡¯t define ¡°sgn¡± in the function ¡°uppertri¡± is that it is inherited from the call of ¡°determinant¡¯.
However, I put ¡°sgn=1¡± so that the function ¡°uppertri¡± works independently.

I checked the function ¡°uppertri¡± and found that it worked fine. Here is a sample file.

\environment MatrixLuacode


\starttext
\getbuffer[luaMatrix]

\startformula\startalign
\startluacode
local mat = {{0, 2, 4, -4, 1},{0, 0, 2, 3 , 4}, {2, 2, -6, 2, 4 }, {2,0 , -6, 9, 7},{2, 2, -6, 2, 4 },{2, 2, -6, 2, 4 }}
-- local mat = {{1,2,3},{3,4,5},{3,4,5},{3,4,5},{3,4,5}}
context.NC("\\text{Given Matrix}\\quad\\Rightarrow\\quad")
context.NC()
matrixOP.write(mat)
context.NR()
context.NC()
context("\\text{Upper Triangular}\\quad\\Rightarrow\\quad")
mat = matrixOP.upperTri(mat)
context.NC()
matrixOP.write(mat)
context.NR()
\stopluacode
\stopalign\stopformula

\stoptext


Sometimes, I got ¡°-0¡± as an entry of matrix after calculation but I couldn¡¯t resolve it(I asked about it to this list before). 

Thank you.

Best regards,

Dalyoung