Operations with symbols / variables

[Andre_AA1]

Hi, 

Is there a way to operate with symbols (variables x, y, etc) on SAS? Like 2x+3x=5x or exp(2*3+1-x/2)=exp(7-0.5*x) ?

I searched for it online and couldnt find anything. And I think it's kind of a long shot, because SAS is more for data analysis, but since some mathematical softwares do it, I thought I'd ask.

[LinusH]

Sure, I mean, symbols are implemented as variables in SAS, and the formulas you provide can be coded in the data step, SQL to name a few places.

Can you give a bit more context how you wish to use this?

[Andre_AA1]

I constructed a model (logistic regression) with 12 explanatory variables, so I have the model function y = f(x_1, x_2, ..., x_12). Besides, I have another function that depends on one of this variables, say z=g(x_1). Now, I need tho solve the equation for x_1:

f(x_1,...,x_12)*g(x_1)=Lambda,

where Lambda is some constant.

As I was writing this reply, I realized it is more than I asked in the original question, but the operating with symbols seemed a good place to start and I didn't find anything online.

[Reeza]

Seems like you want to look into PROC NLIN?

[Andre_AA1]

Isn't this for modelling with nonlinear types of equation? I read some of the documentation and didn't find it related... I wanted the "pure" mathematical expression thats solves the equation.

[Reeza]

Then AFAIK, SAS does not do this.

[ballardw]

You may need to clarify what you mean by your question.

Do you mean if a SAS data set variable contains such calculations can it be used to perform the calculations?

Or do you mean to manipulate the text of a value to a different equivalent form?

Where are these operations stored?

[Reeza]

AFAIK SAS does not simplify mathematical equations, which is my interpretation of your question.

[Ksharp]

Maybe @Rick_SAS knows ?

[Rick_SAS]

In general, it is impossible to solve the equation  f(x_1,...,x_12)*g(x_1)=Lambda for x_1. Symbolic math software (such as Mathematica or the free version at  WolframAlpha.com)  can invert simple equations such as low-order polynomials, and I think that is what you are asking about. No, SAS does not contain a symbolic algebra system.

However, for any specified value of Lambda, you can NUMERICALLY solve for the value of x_1 that satisfies the equation by finding the root (zero) of the equation  f(x_1,...,x_12)*g(x_1) - Lambda = 0. This is a one-dimensional root-finding problem, so can be solved in many ways. See 

• Find the root by using the DATA step
• Find the root in SAS/IML by using the FROOT function