Clear inside a loop

Question

I want to solve a system of differential equations and each time I want to change two parameters. To prevent wrong result I want to clear every assignment after solving the equations in each iteration. I have a Do-loop with two iterator. The problem is that if I use Clear["Global`*"] then the outer iterator will not be accessible to the code inside the loop.

Here is an example:

Do[{Print[a]; Clear["Global`*"];}, {a, 1, 2}, {b, 1, 2}]

Result:

1
a
2
a

As you can see the iterator a is erased for the inner iterator b. How can I resolve this issue?

I expect the outer iterator to be printed each time. There are 4 iteration in total, so I expect to get:

I want both iterators, a and b, in spite of using Clear command to be accessible to the code inside loop. I want to clear everything after each iteration except iterators a and b.

Perhaps a description and removal of the actual symbol clash would be more effective than dropping the big one. Posting the offending code is often useful. — Yves Klett, Jul 01 '14 at 10:27

score 2 · Accepted Answer · answered Jul 01 '14 at 10:38

2

How about this?

Do[{Print[a];
  Map[Clear, DeleteCases[Names["Global`*"], "a" | "b"]]},
 {a, 1, 2}, {b, 1, 2}]

answered Jul 01 '14 at 10:38

Chris Degnen

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1

That gives 1 1 2 2 as well as Do[{Print[a]; Quiet@ClearAll["Global`*"];}, {a, 1, 2}, {b, 1, 2}]. Apparently the OP desires 1 1 1 1. – Öskå Jul 01 '14 at 10:40
@Öskå I am sorry I was wrong. This answer is what I needed. – MOON Jul 01 '14 at 10:42
Without clearing a and b the result should be 1 1 2 2. – Chris Degnen Jul 01 '14 at 10:42
1

Ah, well, ClearAll is enough then :) – Öskå Jul 01 '14 at 10:42
As far as I know what I wrote in my first comment works ;o) – Öskå Jul 01 '14 at 10:45
Could someone add Öskå solution to the answer too? – MOON Jul 01 '14 at 10:46
@yashar It's enough in the comment I guess :) – Öskå Jul 01 '14 at 10:47
@Öskå Could you please explain about the functionality of Quiet? In the Mathematica help it's written that this command prevents messages to be generated. I cannot understand the role of this command here. – MOON Jul 01 '14 at 11:02

Clear inside a loop

1 Answers1