On 3/10/12, Lorenzo Sutton lorenzofsutton@gmail.com wrote:
On 09/03/12 19:18, Quim Llimona wrote:
It's well-known that floats can't be treated the same way as integers... but since PD is aimed at non-engineers and non-scientists I think it would be a good idea to implement the "good" comparison algorithms (i.e. checking against a threshold, etc) inside [==] and so, just to make patching easier. Maybe it's already supposed to behave this way...
No, no...I don't agree (and hope initiating the thread didn't suggest this idea). [==] should be what it says exact comparison. Actually in the patch I was making it would have been simple to put in a [>=] instead which basically *is* a threshold... I just thought it would be nice to point out some float fun given all the discussions :)
Lorenzo.
How about an abstraction that uses <= against 2xepsilon*|input|? That would be a reliable automatic way to ignore single-bit rounding errors. I'm just using this page as a reference: http://en.wikipedia.org/wiki/Machine_epsilon There's two inputs, so I'd choose the largest of them and use that in calculating the threshold. The test patch below just takes a vertical slider from -1e-7 to 1e-7 and adds the value to 0.999 to be compared against. This patch needs a little improvement--it seems to be obeying a threshold which is a little closer to 8.9e-8 (which is greater than the 32-bit machine epsilon.... so it still does what is wanted with a little extra room)
nearly_equal.pd
#N canvas 86 491 682 612 10; #X obj 91 39 inlet; #X obj 137 39 inlet; #X obj 182 39 $1; #X obj 216 39 loadbang; #X obj 94 140 abs; #X obj 98 345 <=; #X obj 139 110 abs; #X obj 185 110 abs; #X obj 93 74 t f f; #X obj 138 74 t f f; #X obj 140 212 >=; #X obj 189 209 <; #X obj 139 145 f; #X obj 186 144 t b f; #X obj 202 244 *; #X obj 140 172 t f f; #X obj 140 244 *; #X obj 94 108 -; #X obj 140 276 +; #X obj 140 308 * 1.192e-07; #X obj 97 391 outlet; #X connect 0 0 8 0; #X connect 1 0 9 0; #X connect 2 0 17 1; #X connect 3 0 2 0; #X connect 4 0 5 0; #X connect 5 0 20 0; #X connect 6 0 12 0; #X connect 7 0 13 0; #X connect 8 0 17 0; #X connect 8 1 6 0; #X connect 9 0 17 1; #X connect 9 1 7 0; #X connect 10 0 16 0; #X connect 11 0 14 0; #X connect 12 0 15 0; #X connect 13 0 12 0; #X connect 13 1 10 1; #X connect 13 1 11 1; #X connect 13 1 14 1; #X connect 14 0 18 1; #X connect 15 0 10 0; #X connect 15 1 11 0; #X connect 15 1 16 1; #X connect 16 0 18 0; #X connect 17 0 4 0; #X connect 18 0 19 0; #X connect 19 0 5 1;
nearly_equal_test.pd
#N canvas 0 25 264 184 10; #X obj 118 79 nearly_equal 0.999; #X obj 38 27 vsl 15 128 -1e-07 1e-07 0 0 empty empty empty 0 -9 0 10 -262144 -1 -1 0 1; #X floatatom 115 135 5 0 0 0 - - -; #X obj 116 18 + 0.999; #X connect 0 0 2 0; #X connect 1 0 3 0; #X connect 3 0 0 0;