| 1 | # Natural logarithm.
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| 2 | #
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| 3 | # Note that we use the mathematics / Javascript / Mathematica
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| 4 | # convention that "log" is indeed the natural logarithm.
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| 5 | #
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| 6 | # In engineering, biology, astronomy, "log" can stand instead
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| 7 | # for the "common" logarithm i.e. base 10. Also note that Google
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| 8 | # calculations use log for the common logarithm.
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| 9 |
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| 10 |
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| 11 | Eval_log = ->
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| 12 | push(cadr(p1))
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| 13 | Eval()
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| 14 | logarithm()
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| 15 |
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| 16 | logarithm = ->
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| 17 | save()
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| 18 | yylog()
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| 19 | restore()
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| 20 |
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| 21 | yylog = ->
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| 22 | d = 0.0
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| 23 |
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| 24 | p1 = pop()
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| 25 |
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| 26 | if (p1 == symbol(E))
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| 27 | push_integer(1)
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| 28 | return
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| 29 |
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| 30 | if (equaln(p1, 1))
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| 31 | push_integer(0)
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| 32 | return
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| 33 |
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| 34 | if (isnegativenumber(p1))
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| 35 | push(p1)
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| 36 | negate()
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| 37 | logarithm()
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| 38 | push(imaginaryunit)
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| 39 | if evaluatingAsFloats
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| 40 | push_double(Math.PI)
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| 41 | else
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| 42 | push_symbol(PI)
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| 43 | multiply()
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| 44 | add()
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| 45 | return
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| 46 |
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| 47 | if (isdouble(p1))
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| 48 | d = Math.log(p1.d)
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| 49 | push_double(d)
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| 50 | return
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| 51 |
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| 52 | # rational number and not an integer?
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| 53 |
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| 54 | if (isfraction(p1))
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| 55 | push(p1)
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| 56 | numerator()
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| 57 | logarithm()
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| 58 | push(p1)
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| 59 | denominator()
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| 60 | logarithm()
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| 61 | subtract()
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| 62 | return
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| 63 |
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| 64 | # log(a ^ b) --> b log(a)
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| 65 |
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| 66 | if (car(p1) == symbol(POWER))
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| 67 | push(caddr(p1))
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| 68 | push(cadr(p1))
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| 69 | logarithm()
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| 70 | multiply()
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| 71 | return
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| 72 |
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| 73 | # log(a * b) --> log(a) + log(b)
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| 74 |
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| 75 | if (car(p1) == symbol(MULTIPLY))
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| 76 | push_integer(0)
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| 77 | p1 = cdr(p1)
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| 78 | while (iscons(p1))
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| 79 | push(car(p1))
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| 80 | logarithm()
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| 81 | add()
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| 82 | p1 = cdr(p1)
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| 83 | return
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| 84 |
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| 85 | push_symbol(LOG)
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| 86 | push(p1)
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| 87 | list(2)
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| 88 |
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