MapAt

Name:
`MapAt - applies a function to some of the elements of its argument`
Synopsis:
```array1 proc array2 MapAt -> array3
```
Examples:
```      [3 4 5 6 7] {dup mul} -2 MapAt    -> [3 4 5 36 7]    [3 [-9 -12] 5 6 7] {dup mul} [2 2] MapAt    -> [3 [-9 144] 5 6 7]    [3 4 5 6 7] {dup mul} [[1] [3]] MapAt    -> [9 4 25 6 7]    [[3 9] 4 [5 -11] 6 7] {dup mul} [[1 2] [3 1]] MapAt    -> [[3 81] 4 [25 -11] 6 7]       [0 0 0 0 0] {1 add} [2 4 5 2 3 2 2 5] 1 1 Partition MapAt    -> [0 4 1 1 2]
```
Description:
```   MapAt successively applies proc to the elements of array1    specified by array2 and replaces the original values by the    return value of proc. The return value array3 has exactly the    same shape as the first argument array1.       Compared to languages like Matlab MapAt constitutes an lhs    assignment operator for constructs like a(i)=f(a(i)), where    i may be an array of indices. However, unlike in Matlab no    temporary object a(i) for the rhs expression is created.    Consequently, if the index ii occurs in array i n times the    final value of a(ii) returned by MapAt is the cumulative effect    of f operating n times on the original value of a(ii):    a(ii) <- f(f(...f(a(ii))...))    n times    In Matlab the result is f(a(ii)), independent of n.    The behavior of MapAt is, for example, useful in counting    processes like the construction of a histogram as shown in the    last example of the examples section.
```
Parameters:
```   array1 is an arbitrarily shaped array. In particular    it does not need to be rectangular.    array2 specifies a multi-dimensional position [i, j,...]    in array1 or a list of positions [ [i1,j1,...], [i2,j2,...], ...].    The same element may be specified multiple times in array2 at    arbitrary positions.       The first element on each level has index 1. Indices can also    be specified counting from the end of the array, in this case the    last element has index -1. Positive and negative indices can    arbitrarily be intermixed.
```
Remarks:
```   This function is an implementation of Mathematica's MapAt function.    Mathematica-style functions in SLI use Mathematica index notation.
```
References:
```   [1] The Mathematica Book V4.0 "Part"
```
Author:
```Diesmann
```
FirstVersion:
```2007.08.12
```
SeeAlso: Source:
`/home/nest/work/nest-2.14.0/lib/sli/mathematica.sli`