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Re: Telling Mathematica that a symbol is going to be a List?


Use definition

m[d_List]:={ { d[[1]], 0, 0}, {0, d[[2]], 0}, {0, 0, d[[3]]}

and then call

m[{d1,d2,d4}]

without any errors.


AES/newspost wrote:

>I want to define a function containing parameters that are going to be 
>elements in a list, e.g. something like
>
>  m := { { d[[1]], 0, 0}, {0, d[[2]], 0}, {0, 0, d[[3]]}
>
>but not define the list of values of  d  until later (and not put the 
>parameters in as explicit arguments of  m  just to keep the appearance 
>less cluttered and typing easier).
>
>If I then give an input line
>
>    m /. {d -> {d1, d2, d3} } // MatrixForm
>
>I get "Part::partd" errors -- but the matrix then displays correctly.
>
>I can of course just Off[] the errors -- but is there a better way.
>
>  
>



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