http://jsoftware.com/help/learning/11.htm
Learning J
Chapter 11: Tacit Verbs Concluded
11.5 Parametric Functions
The following example shows the consequences of nouns being evaluated
and verbs not in an expression for a tacit verb.
A curve may be specified by an equation such as, for example:
y = lambda * x * (1 - x)
This equation describes a family of similar parabolic curves, and
different members of the family are picked out by choosing different
values for the number lambda.
A function to correspond to this equation might be written explicitly as verb P:
P =: 3 : 'lambda * y * (1-y)'
Here lambda is not an argument to function P, but a variable, a
number, which makes a difference to the result. We say that lambda is
a parameter, or that function P is parametric.
x=:0.6 lambda=: 3.0 P x lambda=: 3.5 P x
0.6 3 0.72 3.5 0.84
Now, can we write a tacit version of P taking lambda as a parameter?
lambda is currently 3.5. If we now generate a tacit form of P
tP =: 13 : 'lambda * y * (1-y)'
tP
3.5 * ] * 1 - ]
then we see that lambda is treated as a constant, not a parameter.
This is not what we want.
Further explanation and workarounds follow.
On Sun, July 22, 2012 2:37 pm, Brian Schott wrote:
> Ric,
>
> Thanks for that fact, which I never new.
>
> On Sun, Jul 22, 2012 at 1:48 PM, Ric Sherlock <[email protected]> wrote:
>> When you assign a Tacit verb to a name the value of the nouns in the
>> definition are "compiled" in to the tacit definition. If you use an
>> explicit definition the noun will be reevaluate d each time.
> --
> (B=)
--
Edward Mokurai (默雷/निशब्दगर्ज/نشبدگرج) Cherlin
Silent Thunder is my name, and Children are my nation.
The Cosmos is my dwelling place, the Truth my destination.
http://wiki.sugarlabs.org/go/Replacing_Textbooks
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
