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### 10.4 Root, Exponential and Logarithmic Functions

Option variable: %e_to_numlog

  Default value: `false`

  When `true`, `r` some rational number, and `x` some expression, `%e^(r*log(x))` will be simplified into `x^r` . It should be noted that the `radcan` command also does this transformation, and more complicated transformations of this ilk as well. The `logcontract` command "contracts" expressions containing `log`.

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·

Option variable: %emode

  Default value: `true`

  When `%emode` is `true`, `%e^(%pi %i x)` is simplified as follows.

  `%e^(%pi %i x)` simplifies to `cos (%pi x) + %i sin (%pi x)` if `x` is a floating point number, an integer, or a multiple of 1/2, 1/3, 1/4, or 1/6, and then further simplified.

  For other numerical `x`, `%e^(%pi %i x)` simplifies to `%e^(%pi %i y)` where `y` is `x - 2 k` for some integer `k` such that `abs(y) < 1`.

  When `%emode` is `false`, no special simplification of `%e^(%pi %i x)` is carried out.

      (%i1) %emode;
      (%o1)                         true

      (%i2) %e^(%pi*%i*1);
      (%o2)                          - 1

      (%i3) %e^(%pi*%i*216/144);
      (%o3)                         - %i

      (%i4) %e^(%pi*%i*192/144);
                                sqrt(3) %i    1
      (%o4)                  (- ----------) - -
                                    2         2

      (%i5) %e^(%pi*%i*180/144);
                                 %i          1
      (%o5)                 (- -------) - -------
                               sqrt(2)    sqrt(2)

      (%i6) %e^(%pi*%i*120/144);
                                %i   sqrt(3)
      (%o6)                     -- - -------
                                2       2

      (%i7) %e^(%pi*%i*121/144);
                                  121 %i %pi
                                  ----------
                                     144
      (%o7)                     %e

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·

Option variable: %enumer

  Default value: `false`

  When `%enumer` is `true`, `%e` is replaced by its numeric value 2.718… whenever `numer` is `true`.

  When `%enumer` is `false`, this substitution is carried out only if the exponent in `%e^x` evaluates to a number.

  See also `ev` and `numer`.

      (%i1) %enumer;
      (%o1)                         false

      (%i2) numer;
      (%o2)                         false

      (%i3) 2*%e;
      (%o3)                         2 %e

      (%i4) %enumer: not %enumer;
      (%o4)                         true

      (%i5) 2*%e;
      (%o5)                         2 %e

      (%i6) numer: not numer;
      (%o6)                         true

      (%i7) 2*%e;
      (%o7)                   5.43656365691809

      (%i8) 2*%e^1;
      (%o8)                   5.43656365691809

      (%i9) 2*%e^x;
                                               x
      (%o9)                 2 2.718281828459045

  Categories:Exponential and logarithm functions ·Evaluation flags ·

Function: exp (x)

  Represents the exponential function. Instances of `exp (x)` in input are simplified to `%e^x`; `exp` does not appear in simplified expressions.

  `demoivre` if `true` causes `%e^(a + b %i)` to simplify to `%e^(a (cos(b) + %i sin(b)))` if `b` is free of `%i`. See `demoivre`.

  `%emode`, when `true`, causes `%e^(%pi %i x)` to be simplified. See `%emode`.

  `%enumer`, when `true` causes `%e` to be replaced by 2.718… whenever `numer` is `true`. See `%enumer`.

      (%i1) demoivre;
      (%o1)                         false

      (%i2) %e^(a + b*%i);
                                   %i b + a
      (%o2)                      %e

      (%i3) demoivre: not demoivre;
      (%o3)                         true

      (%i4) %e^(a + b*%i);
                            a
      (%o4)               %e  (%i sin(b) + cos(b))

  Categories:Exponential and logarithm functions ·

Function: li [s] (z)

  Represents the polylogarithm function of order s and argument z, defined by the infinite series

                                       inf
                                       ====   k
                                       \     z
                              Li (z) =  >    --
                                s      /      s
                                       ====  k
                                       k = 1

  `li [1]` is `- log (1 - z)`. `li [2]` and `li [3]` are the dilogarithm and trilogarithm functions, respectively.

  When the order is 1, the polylogarithm simplifies to `- log (1 - z)`, which in turn simplifies to a numerical value if z is a real or complex floating point number or the `numer` evaluation flag is present.

  When the order is 2 or 3, the polylogarithm simplifies to a numerical value if z is a real floating point number or the `numer` evaluation flag is present.

  Examples:

      (%i1) assume (x > 0);
      (%o1)                        [x > 0]

      (%i2) integrate ((log (1 - t)) / t, t, 0, x);
      (%o2)                       - li (x)
                                      2

      (%i3) li [2] (7);
      (%o3)                        li (7)
                                     2

      (%i4) li [2] (7), numer;
      (%o4)       1.248273182099423 - 6.113257028817991 %i

      (%i5) li [3] (7);
      (%o5)                        li (7)
                                     3

      (%i6) li [3] (7), numer;
      (%o6)       5.319257992145674 - 5.94792444808033 %i

      (%i7) L : makelist (i / 4.0, i, 0, 8);
      (%o7)   [0.0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0]

      (%i8) map (lambda ([x], li [2] (x)), L);
      (%o8) [0.0, 0.2676526390827326, 0.5822405264650125,
      0.978469392930306, 1.644934066848226,
      2.190177011441645 - 0.7010261415046585 %i,
      2.37439527027248 - 1.2738062049196 %i,
      2.448686765338205 - 1.758084848210787 %i,
      2.467401100272339 - 2.177586090303601 %i]

      (%i9) map (lambda ([x], li [3] (x)), L);
      (%o9) [0.0, 0.2584613953442624, 0.537213192678042,
      0.8444258046482203, 1.2020569, 1.642866878950322
       - 0.07821473130035025 %i, 2.060877505514697
       - 0.2582419849982037 %i, 2.433418896388322
       - 0.4919260182322965 %i, 2.762071904015935
       - 0.7546938285978846 %i]

  Categories:Exponential and logarithm functions ·

Function: log (x)

  Represents the natural (base e) logarithm of x.

  Maxima does not have a built-in function for the base 10 logarithm or other bases. `log10(x) := log(x) / log(10)` is a useful definition.

  Simplification and evaluation of logarithms is governed by several global flags:

  ``logexpand``

    causes `log(a^b)` to become `b*log(a)`. If it is set to `all`, `log(a*b)` will also simplify to `log(a)+log(b)`. If it is set to `super`, then `log(a/b)` will also simplify to `log(a)-log(b)` for rational numbers `a/b`, `a#1`. (`log(1/b)`, for `b` integer, always simplifies.) If it is set to `false`, all of these simplifications will be turned off.

  ``logsimp``

    if `false` then no simplification of `%e` to a power containing `log`’s is done.

  ``lognegint``

    if `true` implements the rule `log(-n) -> log(n)+%i*%pi` for `n` a positive integer.

  ``%e_to_numlog``

    when `true`, `r` some rational number, and `x` some expression, the expression `%e^(r*log(x))` will be simplified into `x^r`. It should be noted that the `radcan` command also does this transformation, and more complicated transformations of this as well. The `logcontract` command "contracts" expressions containing `log`.

  Categories:Exponential and logarithm functions ·

Option variable: logabs

  Default value: `false`

  When doing indefinite integration where logs are generated, e.g. `integrate(1/x,x)`, the answer is given in terms of `log(abs(...))` if `logabs` is `true`, but in terms of `log(...)` if `logabs` is `false`. For definite integration, the `logabs:true` setting is used, because here "evaluation" of the indefinite integral at the endpoints is often needed.

  Categories:Exponential and logarithm functions ·Integral calculus ·Global flags ·

Function: logarc (expr)

  The function `logarc(expr)` carries out the replacement of inverse circular and hyperbolic functions with equivalent logarithmic functions for an expression expr without setting the global variable `logarc`.

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·Simplification functions ·

Option variable: logarc

  When the global variable `logarc` is `true`, inverse circular and hyperbolic functions are replaced by equivalent logarithmic functions. The default value of `logarc` is `false`.

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·Simplification functions ·

Option variable: logconcoeffp

  Default value: `false`

  Controls which coefficients are contracted when using `logcontract`. It may be set to the name of a predicate function of one argument. E.g. if you like to generate SQRTs, you can do `logconcoeffp:'logconfun$ logconfun(m):=featurep(m,integer) or ratnump(m)$` . Then `logcontract(1/2*log(x));` will give `log(sqrt(x))`.

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·

Function: logcontract (expr)

  Recursively scans the expression expr, transforming subexpressions of the form `a1*log(b1) + a2*log(b2) + c` into `log(ratsimp(b1^a1 * b2^a2)) + c`

      (%i1) 2*(a*log(x) + 2*a*log(y))$

      (%i2) logcontract(%);
                                       2  4
      (%o2)                     a log(x  y )

  The declaration `declare(n,integer)` causes `logcontract(2*a*n*log(x))` to simplify to `a*log(x^(2*n))`. The coefficients that "contract" in this manner are those such as the 2 and the `n` here which satisfy `featurep(coeff,integer)`. The user can control which coefficients are contracted by setting the option `logconcoeffp` to the name of a predicate function of one argument. E.g. if you like to generate SQRTs, you can do `logconcoeffp:'logconfun$ logconfun(m):=featurep(m,integer) or ratnump(m)$` . Then `logcontract(1/2*log(x));` will give `log(sqrt(x))`.

  Categories:Exponential and logarithm functions ·

Option variable: logexpand

  Default value: `true`

  If `true`, that is the default value, causes `log(a^b)` to become `b*log(a)`. If it is set to `all`, `log(a*b)` will also simplify to `log(a)+log(b)`. If it is set to `super`, then `log(a/b)` will also simplify to `log(a)-log(b)` for rational numbers `a/b`, `a#1`. (`log(1/b)`, for integer `b`, always simplifies.) If it is set to `false`, all of these simplifications will be turned off.

  When `logexpand` is set to `all` or `super`, the logarithm of a product expression simplifies to a summation of logarithms.

  Examples:

  When `logexpand` is `true`, `log(a^b)` simplifies to `b*log(a)`.

      (%i1) log(n^2), logexpand=true;
      (%o1)                       2 log(n)

  When `logexpand` is `all`, `log(a*b)` simplifies to `log(a)+log(b)`.

      (%i1) log(10*x), logexpand=all;
      (%o1)                   log(x) + log(10)

  When `logexpand` is `super`, `log(a/b)` simplifies to `log(a)-log(b)` for rational numbers `a/b` with `a#1`.

      (%i1) log(a/(n + 1)), logexpand=super;
      (%o1)                  log(a) - log(n + 1)

  When `logexpand` is set to `all` or `super`, the logarithm of a product expression simplifies to a summation of logarithms.

      (%i1) my_product : product (X(i), i, 1, n);
                                   n
                                 /===\
                                  ! !
      (%o1)                       ! !  X(i)
                                  ! !
                                 i = 1
      (%i2) log(my_product), logexpand=all;
                                n
                               ====
                               \
      (%o2)                     >    log(X(i))
                               /
                               ====
                               i = 1
      (%i3) log(my_product), logexpand=super;
                                n
                               ====
                               \
      (%o3)                     >    log(X(i))
                               /
                               ====
                               i = 1

  When `logexpand` is `false`, these simplifications are disabled.

      (%i1) logexpand : false $
      (%i2) log(n^2);
                                        2
      (%o2)                        log(n )
      (%i3) log(10*x);
      (%o3)                       log(10 x)
      (%i4) log(a/(n + 1));
                                       a
      (%o4)                      log(-----)
                                     n + 1
      (%i5) log ('product (X(i), i, 1, n));
                                     n
                                   /===\
                                    ! !
      (%o5)                    log( ! !  X(i))
                                    ! !
                                   i = 1

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·

Option variable: lognegint

  Default value: `false`

  If `true` implements the rule `log(-n) -> log(n)+%i*%pi` for `n` a positive integer.

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·

Option variable: logsimp

  Default value: `true`

  If `false` then no simplification of `%e` to a power containing `log`’s is done.

  Categories:Exponential and logarithm functions ·Simplification flags and variables ·

Function: plog (x)

  Represents the principal branch of the complex-valued natural logarithm with `-%pi < carg(x) <= +%pi` .

  Categories:Exponential and logarithm functions ·Complex variables ·

Function: sqrt (x)

  The square root of x. It is represented internally by `x^(1/2)`. See also `rootscontract` and `radexpand`.

  Categories:Mathematical functions ·

Next: Trigonometric Functions, Previous: Combinatorial Functions, Up: Mathematical Functions [Contents][Index]