updating jit.matrix inside javascript

hello all,
I've been poundering my brain on tis for quite some time, but I can't seem to find the answer, I'm really hoping someone can help me out here

what i'm trying to do is use a glmultmatrix for a jit.gl.sketch in javascript
I've made the sketch object and set

sketch.glmultmatrix=multMatrix;

I've made a function with the setcell message to fill the multMatrix

I think i need the following to update my matrix

multMatrix.matrixcalc(multMatrix,multMatrix);

but that gives an error saying matrixcalc is not a function.

I'm totally lost here, and I'm wondering if this is a way of doing this altogether?

Also will the sketch automatically check the multMatrix or should i do something there too?

Is there anyone who can explain me what I'm missing?

Best Regards,

Pieter