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 Item Amend m}  _ _ _ Amend

 If m is numeric and z=: m} y , then \$z equals \$m , which equals the shape of an item of y . The atom j{z is j{(j{m){y . For example: ``` y=: a.{~(a.i.'A')+i.4 5 m=: 3 1 0 2 1 y ; m ; m}y +-----+---------+-----+ |ABCDE|3 1 0 2 1|PGCNJ| |FGHIJ| | | |KLMNO| | | |PQRST| | | +-----+---------+-----+ ``` If m is not a gerund, x m} y is formed by replacing by x those parts of y selected by m&{ (an error is signalled if such selection requires fill). Thus: ``` y; '%*'(1 3;2 _1)} y +-----+-----+ |ABCDE|ABCDE| |FGHIJ|FGH%J| |KLMNO|KLMN*| |PQRST|PQRST| +-----+-----+ ``` \$x must be a suffix of \$m{y , and x has the same effect as (\$m{y)\$,x . Thus: ``` y; 'think' 1 2} y +-----+-----+ |ABCDE|ABCDE| |FGHIJ|think| |KLMNO|think| |PQRST|PQRST| +-----+-----+ ```

If m is a gerund, one of its elements determines the index argument to the adverb } , and the others modify the arguments x and y :
 x (v0`v1`v2)} y ↔ (x v0 y) (x v1 y)} (x v2 y) (v0`v1`v2)} y ↔ (v1 y)} (v2 y) (v1`v2)} y ↔ (v1 y)} (v2 y)

For example, the following functions E1, E2, and E3 interchange two rows of a matrix, multiply a row by a constant, and add a multiple of one row to another:
```   E1=: <@] C. [
E2=: f`g`[}
E3=: F`g`[}
f=: {:@] * {.@] { [
F=: [: +/ (1:,{:@]) * (}:@] { [)
g=: {.@]
M=: i. 4 5
M;(M E1 1 3);(M E2 1 10);(M E3 1 3 10)
+--------------+--------------+--------------+-------------------+
| 0  1  2  3  4| 0  1  2  3  4| 0  1  2  3  4|  0   1   2   3   4|
| 5  6  7  8  9|15 16 17 18 19|50 60 70 80 90|155 166 177 188 199|
|10 11 12 13 14|10 11 12 13 14|10 11 12 13 14| 10  11  12  13  14|
|15 16 17 18 19| 5  6  7  8  9|15 16 17 18 19| 15  16  17  18  19|
+--------------+--------------+--------------+-------------------+

```

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