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Student Support Forum: 'Nested Lists,Definition and Evaluation.' topicStudent Support Forum > General > "Nested Lists,Definition and Evaluation."

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Alexander
08/18/05 04:27am

Hello!

Here is simple example of defining list:

b = Table[Symbol["a" <> ToString[i] <> ToString[j]], {i, 2}, {j, 2}];
a11 = IdentityMatrix[2];
b[[1,1]][[1,1]]

Output will be number 1.

Then we type another command:
b[[1,1]][[1,1]]=2

wich cause error message.

If we type ?b the structure of b can be seen:
Global`b
b = {{a11, a12}, {a21, a22}}

And I wonder, how to change elements of aij from b? It's interesing question about how mathematica think things and how evaluate them.

So, the questions are:
1) Why code above produce error message?
2) What difference between b[[1,1]][[1,1]] and
b[[1,1,1,1]] notation?

Here is an example concerning the second question:
This code doesn't produce error:

a11 = IdentityMatrix[2];
b = Table[Symbol["a" <> ToString[
i] <> ToString[j]], {i, 2}, {j, 2}];
b[[1, 1, 1, 1]] = 3

but this does:

a11 = IdentityMatrix[2];
b = Table[Symbol["a" <> ToString[
i] <> ToString[j]], {i, 2}, {j, 2}];
b[[1, 1]][[1, 1]] = 3

Why?

Sorry for my obscure speech, and thanks for your answers!


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Subject (listing for 'Nested Lists,Definition and Evaluation.')
Author Date Posted
Nested Lists,Definition and Evaluation. Alexander 08/18/05 04:27am
Re: Nested Lists,Definition and Evaluation. yehuda ben-s... 08/24/05 2:02pm
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