# Why is there a seperate Math class?

Why does everything have to be Math.(num)? Isn’t num.func more
object oriented-ish?

For example:

(Math.methods - Object.methods).select {|x| Math.method(x).arity ==
1}.each do |x|
?> Numeric.class_eval { ?> define_method(x.to_sym) {
Math.send(x.to_sym, self) } >> }

end
=> [“tan”, “frexp”, “sinh”, “exp”, “acos”, “tanh”, “log”, “asin”,
“acosh”, “cos”, “log10”, “atan”, “erf”, “asinh”, “sin”, “sqrt”, “cosh”,
“erfc”, “atanh”]

5.sqrt
=> 2.23606797749979

Math.sqrt(5)
=> 2.23606797749979

I think the first one, 5.sqrt, looks much better than Math.sqrt(5).

Thanks,
Dan

Daniel F. [mailto:[email protected]] :

# I think the first one, 5.sqrt, looks much better than Math.sqrt(5).

Indeed, but only on the first glance.

Math.sqrt *is the sine function; which in turn has its own set of
properties/behavior among the gazillion of other functions found in
mathematics. You pass only 5 here as the parameter. So it is not really
object for objects sake. We have to bear in mind what object we want to
center our minds on. Here, in this case, the object may be the sine
behavior, and the behavior varies by changing the parameter provided.
And hey, is 5 in degrees or in radians? Maybe that should be
5.radians.sine or sine(5.radians) --just joking kind regards -botp

ps: i do also use 5.sin though. sometimes, i feel it is not good to
stick to traditions especially when i’m teaching my kids ruby. in
programming, i do not want them to think that *it’s the *only way (we
write things)… Welcome to the brave new world of ruby.

# Dan

Daniel F. wrote:

Why does everything have to be Math.(num)? Isn’t num.func more
object oriented-ish?

In addition to the answers by others, what would you do for those math
functions whose arity isn’t 1?

Math.methods(false).select{ |n| Math.method(n).arity != 1 }
#=> [“hypot”, “atan2”, “ldexp”]

All three take two arguments. While 3.hypot(4) might make
sense–given one leg of a right triangle, how long is the hypotenuse to
a given other leg–30.atan2( 40 ) makes little sense to me.

A few exceptions might not make a good arguments against 19 possibly
plausible cases. In my opinion, however, once you have to break the
rule it makes sense to look for a new way to handle all the cases
similarly.

And, personally, I agree with Matz - the trigonometric functions simply
look more correct (to me) as functions that take an argument, not
methods invoked upon a number. That’s purely a matter of taste, though.

On 1/9/07, Phrogz [email protected] wrote:

All three take two arguments. While 3.hypot(4) might make
sense–given one leg of a right triangle, how long is the hypotenuse to
a given other leg–30.atan2( 40 ) makes little sense to me.

hypot and atan are vector methods, so [30, 40].atan2, [3,4].hypot
would be correct in the OO-sense, much like #max and #min are in Array
and not Math (compare to e.g. JavaScript where there is Math.max and
Math.min)

On 1/8/07, Daniel F. [email protected] wrote:

Why does everything have to be Math.(num)? Isn’t num.func more
object oriented-ish?

Also, i forgot to mention, by including the module, you can make
things look very similar to what you’d actually see in equations.

include Math
=> Object
3 * sin(40)
=> 2.23533948143805

Daniel F. wrote:

Why does everything have to be Math.(num)? Isn’t num.func more
object oriented-ish?

Having the math functions in a module means there could be an alternate
module with a different implementation.

Why another implementation of Math::sin?

Well, I notice that some folks on this thread have used the example of
sin(90), probably expecting the argument units to be degrees rather than
radians. There could be an alternate library using degrees:

MathDeg::sin(90) # ==> 1.0

Another example might be a version of Math that used something other
than libm, perhaps something with different precision, or optimized
differently.

The point is that the various math functions (or a particular
implementation of them) belong together more than they belong to
numbers.

Daniel F. wrote:

“acosh”, “cos”, “log10”, “atan”, “erf”, “asinh”, “sin”, “sqrt”, “cosh”,
“erfc”, “atanh”]

5.sqrt
=> 2.23606797749979

Math.sqrt(5)
=> 2.23606797749979

I have to say I’m very happy with that sort of things, as in a program
of my own, (plotting scientific data), the user just can say

ctioga --math ‘sin(x)’

to plot the sine of x.

It would be confusing for a non rubyist to run

ctioga --math ‘x.sin’

Wouldn’t it ? Don’t forget in this particular case, syntax can have
impact on non-programming users… Cheers !

Vince

On 1/10/07, Vidar H. [email protected] wrote:

There are inconsistencies that annoy me with Ruby, though, such as
Math.sin(x) but x.abs

x.abs seems to me a convenience method.

If you’re using irb in math mode or something like this, this might

module Math
def abs(x)
x.send(:abs)
end
end
=> nil
include Math
=> Object
abs(10)
=> 10
abs(-10)
=> 10
abs(-10.2114125)
=> 10.2114125

Bil K. [email protected] writes:

Daniel F. wrote:

Why does everything have to be Math.(num)? Isn’t num.func
more object oriented-ish?

That was one the first questions I had
when I came to the Ruby world.

FWIW, here’s a related answer from Matz,

Hmpf. In my math textbook 1/2 != 0, and there’s no such thing as a
“zeroth” element. (I guess there is some complex tradition precidence
at work.) Steve

Bira wrote, On 1/9/2007 5:36 AM:

+1

Hi,

In message “Re: Why is there a seperate Math class?”
on Tue, 9 Jan 2007 11:21:21 +0900, Daniel F.
[email protected] writes:

|I have to think this is the first time I’ve ever really disagreed with
|matz and don’t really understand his logic.

Probably it’s highly influenced by the languages we speak.
Unfortunately, English is not the only language on Earth.

|If I were to ask someone for the length of the word apples, I would say
|“What is the length of apples?” In ruby, this would be “apples”.length.

I would say “apples no nagasa wa?” in Japanese (nagasa = length).

|If I were to ask someone for the sine of, say, 90, I would say “What is
|the sine of 90?” In ruby, this would be Math.sin(90) even though the
|structure of the sentence is the same as for “apples” above.

I would say “sin(90) wa?”. See? It’s different. Besides that, and far more importantly, Ruby honors UNIX math library
(libm). All functions in Math module are found in libm.

``````          matz.
``````

Let me try to make everybody happy :

class Numeric
Math.methods(false).each { |m|
sm = Math.method(m)
if Math.method(m).arity == 1
define_method m do
sm.call self
end
end
}
end

irb(main):001:0> require ‘math_extend’
=> true
irb(main):002:0> 34.cos
=> -0.848570274784605
irb(main):003:0> Math.cos 34
=> -0.848570274784605

Regards,
Maël Clérambault

Hi,

In message “Re: Why is there a seperate Math class?”
on Wed, 10 Jan 2007 07:52:15 +0900, Steven L. [email protected]
writes:

|Hmpf. In my math textbook 1/2 != 0, and there’s no such thing as a
|“zeroth” element. (I guess there is some complex tradition precidence
|at work.)

Yep, try require ‘mathn’.

``````          matz.
``````

“Erik V.” [email protected] writes:

Sin is an action WITH 90.

even though the structure of the sentence is the same as for
“apples” above.

To me, it’s not.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

I tend to agree. Length can be interpreted as part of, or an attribute
of the object (string) apples. Sin is an action in a class of
mathematical
operations which can operate on instances from a class of numbers.

Tim

On 1/9/07, William J. [email protected] wrote:

See the similarity? However, Ruby, a programming language, doesn’t
need to emulate English.

The way it’s done now (sin(90), cos(90), etc.) makes sense because
it’s similar to the actual mathemathical notation I learned back in
grade school. I find it easier to parse than 90.sin, especially when
the argument is actually an expression rather than a constant number.

}

You gotta love it! A language which really does allow you to easily
modify it
to what you want it to look like and fit with houw yo want to think
problem. Now nobody is right or wrong - its just a question of taste
and
individual thinking style.

Tim

Erik V. wrote:

Sin is an action WITH 90.
Very crooked thinking. Consider

%w( the ruby mafia strikes again ).sort

Is ‘sort’ a property of %w( the ruby mafia strikes again ) ?

even though the structure of the sentence is the same as for
“apples” above.

To me, it’s not.

What is the zig of zag?
What is the boo of hoo?

See the similarity? However, Ruby, a programming language, doesn’t
need to emulate English.

If I were to ask someone for the length of the word apples, I
would say “What is the length of apples?” In ruby, this would
be “apples”.length.

Length is a property OF “apples”.

If I were to ask someone for the sine of, say, 90, I would
say “What is the sine of 90?” In ruby, this would be
Math.sin(90)

Sin is an action WITH 90.

even though the structure of the sentence is the same as for
“apples” above.

To me, it’s not.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

Hi –

On Tue, 9 Jan 2007, Gregory B. wrote:

but 90.sin * 10 looks as ugly as can be.

The expression you’re looking for is “ugly as sin” David

Daniel F. wrote:

Why does everything have to be Math.(num)? Isn’t num.func more
object oriented-ish?

That was one the first questions I had
when I came to the Ruby world.

FWIW, here’s a related answer from Matz,