[R] Adding and Multiplying two Unevaluated Expressions

["Benjamin Müller"]

HI,

As I'm trying to compute Taylor series, I'm having problems in adding and multiplying unevaluated expressions. I searched for a solution but found none.

my Taylor function works fine for evaluating functions as you can see here:


rTaylorVal=function(exp,x0,dx,n) {

ls=list(x=x0)

newexp=eval(exp,ls)

exp0=exp

for (i in 1:n){
exp0=D(exp0,"x")
newexp=newexp+eval(exp0,ls)/factorial(i)*dx^i
}

return(newexp)

}

Where exp is an expression like exp=expression(x^2*sin(x)), x0 is the startvalue, dx the difference between startvalue and searched value and n is the length of the series.

So I tried to remove dx as a value, to get a Taylor series expression, but it doesn't work as simple multiplication (*) and accumulation (+) is not good for expressions.

That's my point so far, now my question:

Is it actually possible to add and/or multiply expressions, and how?

Thank you so far.

Benjamin Müller
Geographer (B.Sc.)


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