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How do you control evaluation when using apply?

• To: mathgroup at smc.vnet.net
• Subject: [mg130799] How do you control evaluation when using apply?
• From: Brentt <brenttnewman at gmail.com>
• Date: Thu, 16 May 2013 03:28:00 -0400 (EDT)
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• Delivered-to: l-mathgroup@wolfram.com
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Why does this work

In[0]: = jacobianFunction[func_, vars_List] := Module[{f},
   f = Function[Evaluate[vars], Evaluate[D[func, {vars}]]];
  f
   ];
jacobianFunction[{Sin[x y], Cos[x + y]}, {x, y}] @@ {10, 2}

out[0]:= {{2 Cos[20], 10 Cos[20]}, {-Sin[12], -Sin[12]}}

But this does not (the goal is to make the function take a point as an
argument)


In[0]: = jacobianFunction[func_, vars_List] := Module[{f},
   f = Evaluate[Function[Evaluate[vars], Evaluate[D[func, {vars}]]]];
  f@@ # &
   ];
jacobianFunction[{Sin[x y], Cos[x + y]}, {x, y}][{10, 2}]



I can't get f@@ # & to evaluate properly (I've tried wrapping it in
ReleaseHold and evaluate statements, nothing seems to get it to evaluate.

I know I can just rewrite the function to take the point but I'm just
curious why it won't work.

• Follow-Ups:
  • Re: How do you control evaluation when using apply?
    • From: Christoph Lhotka <christoph.lhotka@univie.ac.at>