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It starts like all good stories, I have a matrix A and I want to find the max, sometimes of the whole thing or sometimes along the rows.

var dom = {1..2, 1..5};
var m: [dom] real;
m[1,..]  = [1.0, 2.0, 3.1, 4.8, 5.6];
m[2,..]  = [2.0, 3.0, 4.1, 5.8, 6.6];
writeln(m);
writeln(max(m));

But there's no love here, it just poops on me:

maxy.chpl:5: error: unresolved call 'max([domain(1,int(64),false)] real(64))'
$CHPL_HOME/modules/internal/ChapelBase.chpl:614: note: candidates are: max(x, y)

Should I use reduce or is there some easier syntax?

Brian Dolan
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1 Answers1

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Using a max reduction is the easiest way to accomplish this today:

var mx = max reduce(m);

However, for the problem size shown in the example, a parallel max reduction may be overkill. If performance matters, it may be better to write your own proc max(arr: []) procedure that iterates over the array and finds the largest element.

Chapel already supports a built-in max() procedure for variadic arguments, but it does not support arrays. In answering this question, I wonder if it should...

ben-albrecht
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