[Jprogramming] Evaluating a Gerund Array

[Jon Hough]

Apologies,Outlook.com is killing my line endings. My example in my second question should be
len =: # G  output =. ''  for_j i. len  do. output =.  output + ((j{list)&*@:(G`:6))  end. output 
> From: jghough at outlook.com
> To: programming at jsoftware.com
> Date: Sun, 19 Apr 2015 09:13:25 +0100
> Subject: Re: [Jprogramming] Evaluating a Gerund Array
> 
> Roger, Raul,
> Thanks. Raul's answer is essentially what I needed. And I now have Learning J Chapter 14 open in my browser .
> I am still unsure about a few things, hopefully someone can clear these up.
> 1. If I have my nxn gerund array and I want to evaluate it on a list of n items, such that the first row takes the first item, the second row takes the second item etc.
> e.g.  (*:`%: ,. +:`^) VRB 1 2
> should evaluate to
> 1 14 7.38906
> where VRB is some verb. Learning J, 14.3.1 has a similar example but in that case VRB = `:0 and it evaluateseach verb for the whole list. At first I thought I could do something like (`:0)"(1 0) but I still get unwanted results, namely, in the above case, I get 2x2x2 matrix as output. My workaround is just to take only the desired rows from the output.
> 2. This problem is a little bit more abstract. 
> If I have a list of gerunds (1D this time), and I want to modify each verb in the gerund in some way, and then return the sum of the verbs, I am not sure how to do this.
> For example, if G =:  *:`+:`^  and list =. 3 4 5
> I want an adverb or conjunction that returns a verb of the form (3&*@:*:) + (4&*@:+:) + (5&*@:^) 
> My attempt was to do
> len =: # G output =. '' for_j i. len do. output =. output + ((j{list)&*@:(G`:6)) end. output 
> This is getting me nowhere however. I am actually not sure why it fails. One problem I am guessing exists is in the line output =. '' , which I used to 'initialize' the output verb. I am unsure if this is legal though.
> Regards,Jon
> 
> > Date: Sun, 19 Apr 2015 08:35:34 +0100
> > From: rs at rogerstokes.free-online.co.uk
> > To: programming at jsoftware.com
> > Subject: Re: [Jprogramming] Evaluating a Gerund Array
> > 
> > Maybe "Learning J" section 14.3.1 might be useful.
> > 
> > 
> > 
> > On 19/04/2015 06:51, Jon Hough wrote:
> > > My problem is slightly more complicated than the one I am giving in the example,but in essence the problem is, given a 2x2 array of gerunds, and anumber, how can I return a 2x2 array of the gerunds evaluated for the number.
> > > e.g.
> > >
> > > arr =: *:`%:
> > >
> > >
> > >
> > >     arr2 =: +:`^
> > >
> > >
> > > mat =. arr ,. arr2
> > >
> > >
> > > list =. 4 3
> > >
> > >
> > > I can evaluate individual cells thusly
> > >
> > >
> > >
> > >
> > > ((0{0{mat)`: 6) 4
> > >
> > >
> > > But would like a single expression that would yield the result, for example (input = 4):
> > >
> > >
> > > 16 2
> > > 8  54.5982
> > >
> > >
> > > I cannot seem to get an expression that works. To add slightly to the complexity, my actual problem involves an
> > > arbitrary nxn matrix.
> > >
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