Erratic behavior with complex arithmetic, e.g., sin(z) returns NaN

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Sat, 06/05/2021 - 06:00 am

My code is producing unexpected results when taking the sine of a complex number.  I wrote the following test function to research the problem.

​Function testsine()
variable /c  a

a=cmplx(0,1)

print "a= ", a
print "sin(a)= ", sin(a)
print "sin(sqrt(-1))= ", sin(sqrt(-1))
end

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​

The results printed in the Command Window are pasted here:

•testsine()
  a=   (0,1)
  sin(a)=   0
  sin(sqrt(-1))=   NaN

The built-in sine function is not handling complex numbers as the manual leads me to believe, i.e., sin(x+iy)=sin(x)cosh(y)+ i cos(x)sinh(y). Shouldn't this have produced the result (0, 1.1752) in both cases above, i.e., the sin(a) and sin(sqrt(-1))? 

This is rather a 'problem' of the print command not expecting a complex number unless explicitly getting handed one. Try this:

Function testsine()
    variable/c a,b,c

    a=cmplx(0,1)
    b=sin(a)
    c=sin(sqrt(-1))

    print "a= ", a
    print "sin(a)= ", b
    print "sin(sqrt(-1))= ", c
End

Will give:

•testsine()
  a=   (0,1)
  sin(a)=   (0,1.1752)
  sin(sqrt(-1))=   (0,1.1752)

 

June 5, 2021 at 07:15 pm - Permalink

print/C also solves the problem easily

Function testsine()
variable /c  a

a=cmplx(0,1)

print/C "a= ", a
print/C "sin(a)= ", sin(a)
end

with result

•testsine()
  a=   (0,1)
  sin(a)=   (0,1.1752)

 

June 6, 2021 at 06:16 am - Permalink