Re: Using variable name as string AND value ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg106983] Re: Using variable name as string AND value ?*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sat, 30 Jan 2010 07:13:24 -0500 (EST)

On 1/29/10 at 7:47 AM, pkshreeman at gmail.com (Paul) wrote: >In process of writing a certain routine, I am puzzled to how to >write this concept into Mathematica format. What I need to do is be >able to extract both string and values, p1 as parameter number one, >p2 as parameter number 2, etc...and I have to put all values into >one single matrix to do some mathematical operations. However, I >also have to call a function that depends on using the variable >p1,p2, so I have to reassign the values back as following >p1=10 p2=23 ... >Parameter={p1,p2,......} and perhaps Strings={"p1","p2",...}? >After mathematical manipulations of matrix Parameter is done, I can >manually do this >p1=Parameter[[1]], p2=Parameter[[2]], .... >But I need to be able to do it with Do Loop such as >Do[ String[[j]]=Parameter[[j]] ,{j,1,PL}] >The problem is that this approach doesn't work in Mathematica. Here is a way to do what you want. First I will create a list of parameter names and values to be assigned to them In[13]:= parameterNames = {"a", "b", "c"}; parameterValues = {1, 2, 3}; Then I will assign the values to the paramters In[15]:= Evaluate[ToExpression[parameterNames]] = parameterValues; and to show the parameters have the assigned values In[16]:= {a, b, c} Out[16]= {1,2,3} Now, this works as written only if the parameters {a, b, c} do not exist at the time the Evaluate[... is executed. What I am doing is using ToExpression to convert the list of strings (parameter names) to symbols Mathematica can assign values to. I use Evaluate to force creation of a list of symbols. Without the Evalaute, Mathematica will issue a error message saying you cannot assign values to ToExpression. =46inally, the = operation assigns the values. It is not necessary to use a looping construct such as Do since Set ("=") threads over its arguments.