This is a subset of a larger sheet. Delta T should be 0, 15, 15 and I get 0, 23, 15. I zeroed out the first heat input and got a large imbedded matrix for unknown reason, that is secondary SMath.smz (5,52 KiB) descargado 1245 vez(es).

Wrote

... and got a large imbedded matrix for unknown reason ...

It carries 'i' from previous use and it has to be cleared in some way.
That is one of many cases of shadow in context, very annoying has it
does not clear the previous matrix.

ElsidDoctored.sm (10,56 KiB) descargado 1176 vez(es).

Appears to carry everything though and just evaluates the last value
Forgot to post. I changed q.w to check values on the top SMath.smz (5,62 KiB) descargado 1209 vez(es).

It's in the loop. If I write an equation dt[1:f.dtv(1) above the program, I get one value array. As I scroll it down, it becomes a 3 value array

Jean, it should not clear the matrix, but build it. Maybe look into stacking it

Looks like it was a structure in the program. I had a "double" program line to start the loop. Cleaned it up and appears to work correctly. Input is always welcome
SMath.smz (5,71 KiB) descargado 1240 vez(es).

Wrote

Maybe look into stacking it

SHOULD BE 15, 15 and .0017. What's wrong?
Just collect as you figure it should be.

SMath [2].smz (5,87 KiB) descargado 992 vez(es).