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sequencerakusignificant-digitsrational-number

Specify the number of decimal digits on the explicit generator of a sequence in Raku

I've written a simple code:

sub euler-ex ($x) of Seq {
   1, { $x**++$ / [×] 1 .. ++$ } ... Inf }
say " 5: " ~ euler-ex(5)[^20]  ~ " = " ~ [+](euler-ex(5)[^20]);

The output:

5: 1 5 12.5 20.833333 26.041667 26.041667 21.701389 15.500992 9.68812 5.382289 2.6911445 1.22324748 0.50968645 0.19603325 0.07001187499 0.023337291662 0.0072929036444 0.00214497166011 0.000595825461143 0.000156796173985 = 148.41310786833832

How to specify the number of digits on that output, i.e. on the decimals coming out of the explicit generator of the sequence?

Solution

  • You can change the last line to

    say " 5: " ~ euler-ex(5)[^20].fmt("%0.10f")  ~ "=" ~ [+](euler-ex(5)[^20]).fmt("%0.10f");

    and get output like

     5: 1.0000000000 5.0000000000 12.5000000000 20.8333333333 26.0416666667 26.0416666667 21.7013888889 15.5009920635 9.6881200397 5.3822889109 2.6911444555 1.2232474798 0.5096864499 0.1960332500 0.0700118750 0.0233372917 0.0072929036 0.0021449717 0.0005958255 0.0001567962=148.4131078683

    You might be interested to know that this sequence is generating Rats, so you could get the exact value if you want. You can see the "raw" values with

    dd euler-ex(5)[^20];

(1, 5.0, 12.5, <125/6>, <625/24>, <625/24>, <3125/144>, <15625/1008>, <78125/8064>, <390625/72576>, <390625/145152>, <1953125/1596672>, <9765625/19160064>, <48828125/249080832>, <244140625/3487131648>, <244140625/10461394944>, <1220703125/167382319104>, <6103515625/2845499424768>, <30517578125/51218989645824>, <152587890625/973160803270656>)