numeric time integral - cumulative sum

Hello everbody,

my problem is about combustion reaction in comsol. I want to burn a porous layer of dust. the problem of the reactive flow in porous media toolbox is, that all species are fluids, and therefore my solid carbon is moving. The oxygen flow is modeled by this toolbox and a reaction rate is calculated.

My idea is, o define a variable "c_0" and subtract the carbon loss every timestep.

something like: c(t) = c_0 - cumsum(reactionrate*timestep)

the carbon concetration c(t) should influence the prorosity, heat capacity etc. of the bulk material.

mybe iam off the track or biased my matlab - but i have no idea how to solve this.

thanks in advance for your help.