topic Re: Multiplying floating point numbers in SAS Programming

Multiplying floating point numbers

SuryaKiran — Thu, 06 Jul 2017 01:04:03 GMT

Hi SAS Users,

Today I came across very weird issue in SAS. I just multplied two floating point values and the result is not accurate to actual values.

If we calculate 0.014x88683.537=1241.569, but SAS give different answer.

DATA test2;
set test;
Mul=num1*num2;
RUN;

Re: Multiplying floating point numbers

WarrenKuhfeld — Thu, 06 Jul 2017 01:16:46 GMT

Use a format like best16. instead of 5.3 and 12.3 and you will get values closer to the true values. Multiple them and see if you get something closer to the expected results.

Re: Multiplying floating point numbers

SuryaKiran — Thu, 06 Jul 2017 01:22:13 GMT

Still the same results after using best16.

Re: Multiplying floating point numbers

WarrenKuhfeld — Thu, 06 Jul 2017 01:27:36 GMT

The SAS product will be the same. The point is if you multiply the numbers together using a calculator, your results will come closer than they did before.

Re: Multiplying floating point numbers

SuryaKiran — Thu, 06 Jul 2017 01:43:35 GMT

Figured out the issue: num1 is shown as rounded to 3 decimal values, but when performing the calculation it is not rounded to 3 decimals.

Re: Multiplying floating point numbers

WarrenKuhfeld — Thu, 06 Jul 2017 01:46:20 GMT

Right. That is why I wanted you to display the numbers with more precision before multiplying them together to compare to the product that SAS reports.

Re: Multiplying floating point numbers

ChrisNZ — Thu, 06 Jul 2017 02:03:45 GMT

SAS gives the correct answer for your example.

data t;
x=0.014*88683.537;

putlog x= 32.16;
run;

x=1241.5695180000000000

Go to https://www.wolframalpha.com/input/?i=0.014x88683.537

for a calculation with many more digits than SAS or your calculator will display.