topic Betreff: Giving a True when it should be nil in Visual LISP, AutoLISP and General Customization Forum

Giving a True when it should be nil

marc_pepin — Mon, 01 Oct 2018 17:19:49 GMT

I got a routine with the line (/= (nth 4 item) 1.5) which return "T" for every real that (nth 4 item) return even 1.5???

Does anyone ever experience that?

Re: Giving a True when it should be nil

dbhunia — Mon, 01 Oct 2018 18:05:51 GMT

if (nth 4 item) return 1.5??? (say 1.55555)

then (/= (nth 4 item) 1.5) means (/= 1.55555 1.5) always return "T"

Re: Giving a True when it should be nil

marko_ribar — Mon, 01 Oct 2018 18:07:04 GMT

Your (nth 4 item) is not exactly 1.5... Check it with (rtos (nth 4 item) 2 50)... If it returns some numbers after 1.5, then your check is wrong, try changing it to (not (equal (nth 4 item) 1.5 fuzz))... If number from (nth 4 item) is in the fuzz range near 1.5 this fix should return valid check value - nil (not T)...

Re: Giving a True when it should be nil

Kent1Cooper — Mon, 01 Oct 2018 18:09:07 GMT

One of your values that displays as 1.5 may actually be 1.499999999999308 or 1.50000000000276 or something. Comparing real numbers, which can result from various kinds of calculations and extractions that can have such tiny differences, should be done using the (equal) function with a fuzz factor:

(not (equal (nth 4 item) 1.5 1e-6))

Betreff: Giving a True when it should be nil

cadffm — Mon, 01 Oct 2018 18:10:41 GMT

They are not the same..

(Rtos (nth 4 item) 2 15) , is it 1.500000000000000 ?

Use function equal [F1]

Re: Giving a True when it should be nil

Kent1Cooper — Mon, 01 Oct 2018 18:15:29 GMT

@marko_ribar wrote:

.... (rtos (nth 4 item) 2 50) ....

[Don't bother with asking for 50 decimal places. 16 is the most you're ever going to wring out of it.]