Re: Unevaluated values of a[[i]]+b[[j]]

*To*: mathgroup at smc.vnet.net*Subject*: [mg65235] Re: [mg65211] Unevaluated values of a[[i]]+b[[j]]*From*: "David Park" <djmp at earthlink.net>*Date*: Sun, 19 Mar 2006 03:19:12 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Alexandre, For low level controlled evaluation in steps you could use the ExpressionManipulation package from my web site below. Needs["Algebra`ExpressionManipulation`"] a = {3, 4, 4}; b = {4, 3, 8}; To keep the output in the posting short I will just evaluate a single composite case from your examples, perhaps with more detail than you might want. The HoldForm header, of course, does not display in the actual output. HoldForm[a[[i]] + b[[j]] + a[[i]]/b[[j]]] % /. {i -> 1, j -> 3} % // EvaluateAtPattern[a | b] % // EvaluateAtPattern[Part[__]] % // ReleaseHold HoldForm[a[[i]] + b[[j]] + a[[i]]/b[[j]]] HoldForm[a[[1]] + b[[3]] + a[[1]]/b[[3]]] HoldForm[{3, 4, 4}[[1]] + {4, 3, 8}[[3]] + {3, 4, 4}[[1]]/{4, 3, 8}[[3]]] HoldForm[3 + 8 + 3/8] 91/8 The EvaluateAtPattern command allows you to evaluate a held expression at specific patterns. There is also an EvaluateAtPosition command that allows evaluation at specific positions. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Alexandre Costa [mailto:amscosta at uem.br] To: mathgroup at smc.vnet.net Dear group, Suppose a have a = {3,4,4} and b = {4,3,8}. I want to see the Unevaluated numerics values of a[[i]]*b[[j]], a[[i]]+b[[j]], a[[i]]/b[[j]], a[[i]] - b[[j]]. The NonCommutativeMultiply operator (**) solves the case of a[[i]]*b[[j]]. But suppose I want to extend that NonCommutativeMultiply operator (**) to others operations: +, -, / , i.e., see the Unevaluated numeric values of a[[i]]+b[[j]], a[[i]]/b[[j]], a[[i]] - b[[j]]. Does anybody have a clue how to do this ? Suppose I have the expression for the roots of the quadratic equation: - b[[index]]^2 + Sqrt[delta]/2*a[[index]] How can I see at once all the numeric values unevaluated on that expression. In short words, I have lenghtly expressions(with sums,subtraction,divisions and multiplications and powers) and I want to check each numeric value of each term in the original unevaluated formula containing elements such as a[[index]] . I was thinking in a operator or function to solve all this issue. Any help is very welcome, Thanks, Alex