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#1 Colombia

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Posted 11 May 2007 - 11:38 PM

Hey to everybody


I need some help with this code:


require("cas")
local y,z
y={"x+y=3","y^2=4"}
z=cas.solve(y,"{x,y}")
print(z)
:banghead:

However, the next code works very well

require("cas")
local y
y=cas.solve({"x+y=3","y^2=4"},"{x,y}")
print(y)

If anyone knows why I can?t put ,just, the variable into the solve function? I will apreciated.

#2 Orwell

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Posted 12 May 2007 - 08:48 PM

Actually the correct code is

require("cas")
local y
y=cas.solve("{x+y=3, y^2=4}","{x,y}")
print(y)
It's completely different than what you wrote ;)

You have to remember something : the CAS only understands numbers, strings, and CAS expressions.
You cannot pass a Lua table to a CAS function.

"{x+y=3,y^2=4}" is a string, you can give it as argument.
But {"x+y=3","y^2=4"} is a Lua table with two strings, and the CAS does not understand it.

If you really want to give a list with 2 expressions as strings, write something like
exp1 = "x+y=3"
exp2 = "y^2=4"
y=cas.solve( "{" .. exp1 .. "," .. exp2 .. "}", "{x,y}")
and NOT
y=cas.solve( {exp1, exp2}, "{x,y}")
which is incorrect.

When you gives a number or a CAS expression as parameter of a CAS function, it is actually transformed into a string. But tables aren't converted in a comprehensible way for the CAS (by default; this can be changed). :)

#3 Orwell

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Posted 12 May 2007 - 09:26 PM

When you gives a number or a CAS expression as parameter of a CAS function, it is actually transformed into a string. But tables aren't converted in a comprehensible way for the CAS (by default; this can be changed). :)

For those who could be wondering, here is a trick to do that:

The idea is to change the way the tables are converted to strings (for example when you print it or when you use it in a CAS expression). We can define a function to do that, by changing the lists' metatables:

function caslist(list)
  meta = getmetatable(list) or {}
  meta.__tostring=function()
	 local s = "{"
	 local notfirst = false
	 for _,v in ipairs(list) do
	   if notfirst 
		 then s = s.."," end
	   s = s .. v
	   notfirst = true
	 end
	 return s .. "}"
	end
  setmetatable(list,meta)
  return list
end
With this you can create and use lists like this:

exp1 = "x+y=3"
exp2 = "y^2=4"
y=cas.solve( caslist{exp1, exp2}, "{x,y}")

Note: remember that with CPLua,
cas.foo(arg1,arg2,...)
is just syntactic sugar for
cas("foo(" .. tostring(arg1) .. "," .. tostring(arg2) ..   ...  .. ")")
:P

#4 Colombia

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Posted 12 May 2007 - 11:46 PM

Thanks Orwell.
I understood all

#5 Orwell

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Posted 13 May 2007 - 08:58 AM

You're welcome ;)

Just a word about my second post: unfortunately it does not seem to work as it should :huh:
I've found where the problem comes from, it should be fixed in th next version :)




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