Hi Nacho,
I wouldn't throw an error because otherwise one must know beforehand that an
equation is non-resolvable or must use #on:do: everywhere.
Since that when you ask to resolve an equation you get back a collection of
solutions, a non-resolvable equation could just return an empty collection,
couldn't it?.
If you really want to consider that asking to resolve a non-resolvable
equation is an error, another solution would be to provide a #rootsIfNone:
method. That's a common pattern in Smalltalk.
I would also rename 'checkNegative' to 'discriminant', because it's not
obvious to see what that variable represents at first glance.
Very good points. I came up with a third draft. This is evolving good!
Thanks
Nacho
"The idea is to have a class to calculate quadratic equations.
This second third still only calculates real roots (leaving aside imaginary
roots).
But thanks to Damien Cassou, and Camille Teruel has a better style.
A QuadraticEquation is a class used to solve Quadratic Equations of the
form: ax^2 + bx + c = 0, where a is not 0.
You can set the coefficients using the following method
setQuadraticCoefficient: linearCoefficient: constant:"
Object subclass: #QuadraticEquation
instanceVariableNames: 'quadraticCoefficient linearCoefficient constant
roots'
classVariableNames: ''
category: 'IS-Math'
"I create accessors (only getters for each term) and then the following
method to set the terms"
setQuadraticCoefficient: aNumber1 linearCoefficient: aNumber2 constant:
aNumber3
quadraticCoefficient := aNumber1.
linearCoefficient := aNumber2.
constant := aNumber3
QuadraticEquation>>calculateRoots
| discriminant |
discriminant := linearCoefficient squared - ( 4 *
quadraticCoefficient *
constant).
discriminant >= 0
ifFalse: [ ^ self rootsIfNone ]
ifTrue: [ ^ self solveRoots: discriminant]
QuadraticEquation>>solveRoots: aTerm
| rootA rootB |
roots := OrderedCollection new.
rootA := (linearCoefficient negated + aTerm sqrt) / (2 *
quadraticCoefficient).
rootB := (linearCoefficient negated - aTerm sqrt) / (2 *
quadraticCoefficient).
roots add: rootA; add: rootB.
^ roots
QuadraticEquation>>rootsIfNone
^ 'No real solution for the equation'
" Example: -3x^2+2x+2=0
an OrderedCollection(-0.5485837703548636 1.2152504370215302)
print(it)
| anEquation |
anEquation := QuadraticEquation new.
anEquation setQuadraticCoefficient: -3 linearCoefficient: 2 constant:
2.
anEquation calculateRoots."
-----
Nacho
Smalltalker apprentice.
Buenos Aires, Argentina.
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