# How do CAS evaluate derivatives

by matqkks
Tags: derivitive, linear algebra, transformations
 P: 145 How do CAS systems and programmable calculators evaluate the derivative of a function? Do they use matrix representation of linear transformations?
 Sci Advisor P: 2,892 I don't know the answer, but you should specify whether you are asking how they evaluate derivatives numerically or how they evaluate them symbollically. Is the result of the evaluation a formula? Or a graph? Or a numerical table?
 P: 145 Sorry for being vague but I meant symbolically.
P: 71

## How do CAS evaluate derivatives

I suspect that they convert whatever expression you want to differentiate into taylor series, differentiate (in the obvious way), then match the result to a taylor series that represents an elementary function and substitute back. Maybe not, but I can't imagine how else it would be done.
 P: 696 From what I heard CAS stores the information as a directed graph. In Mathematica you can use the FullForm command to see it directly for example $\sin(x^2)+3$ would be Plus[3,Sin[Power[x,2]]] It then has rules for how to manipulate these objects. So the derivative operator D (I'm assuming wrt x) interacts with Plus via the rule D[Plus[f,g]] = Plus[D[f],D[g]] Mathematica knows that 3 is constant and so D[3]=0. It then reduces Plus[0,?] to just ?. So we now have D[Sin[Power[x,2]]] It allies its chain rule and is programmed so that D[Sin] = Cos: Multiply[Cos[Power[x,2]],D[Power[x,2]]] And we know that the derivative of Power[x,2] as Multiply[2,x]

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