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## Test file for Hurwitz.

The output of the test file is a simple sequence of printed `ok`s, unless a test fails, in which case diagnostic information is printed.

```interface(echo=1):
with(share):
Im(c) := 0: 	  # An old method of assuming c to be real.
p1 := z^2 + z + 1:
Hurwitz(p1,z):
if "=true then print(ok) else print(") fi:

alias(h=Hurwitz):
p2 := 3*z^3 + 2*z^2 + z + c:
h(p2,z,'s2','g2'):
if "=FAIL then print(ok) else print(") fi:

s2:
if "=[3/2*z,-4*z/(-2+3*c),-1/2*z*(-2+3*c)/c] then print(ok) else print(") fi:

g2:
p3 := 4*z^4 + z^3 + z^2 + c:
h(p3,z,'s3','g3'):
if "=FAIL then print(ok) else print(") fi:

s3:
if "=[0,4*z,z,-z/c,-z] then print(ok) else print(") fi:

g3:
p4 := z^5 + 5*z^4 + 4*z^3 + 3*z^2 + 2*z + c:
h(p4,z,'s4','g4'):
s4:
if s4[3]=289/5*z/(1+5*c) then print(ok) else print(s4[3]) fi:

g4:
Im(d) := 0:
p5 := p2 + I*d:
h(p5,z,'s5','g5'):
if "=FAIL then print(ok) else print(") fi:

s5:
g5:
if g5=1 then print(ok) else print(g5) fi:

p11 := expand((c*z^2 + 1)*(z+1)*(z^2 + 2*z + 2)):
h(p11,z,'s11','g11'):
s11:
g11:
if g11 = c*z^2 + 1 then print(ok) else print(g11) fi:

p13 := 1 + z + z^3:
h(p13,z,'s13','g13'):
if "=false then print(ok) else print(") fi:

s13:
g13:
p14 := 1 + z + c*z^3:
h(p14,z,'s14','g14'):
if "=FAIL then print(ok) else print(") fi:

s14:
g14:
p15 := 1 + z + z^4:
h(p15,z,'s15','g15'):
if "=false then print(ok) else print(") fi:
```
```s15:
g15:
p16 := 1 + x + c*x^4:
h(p16,x,'s16','g16'):
if "=FAIL then print(ok) else print(") fi:

s16:
g16:
```
From [, p. 45,]. There is a typo on the page, found using Maple.
```Lanczos_1 := x^4 + 7.6*x^3 + 23.34*x^2 + 38.44*x + 37.40:
Hurwitz(Lanczos_1,x,'s','g'):
if "=true then print(ok) else print(") fi:

s:
g:
```
From [, p. 46,].
```Lanczos_2 := x^6 + 4.24*x^5 + 8.5*x^4 + 10.27*x^3 + 8.09*x^2 + 3.96*x + 0.98:
Hurwitz(Lanczos_2,x):
if "=true then print(ok) else print(") fi:

Lanczos_3 := expand( (x^2-0.6*x+1)*Lanczos_2 ):
Hurwitz(Lanczos_3,x):
if "=false then print(ok) else print(") fi:
```
From [, p. 47,].
```Lanczos_4 := x^6 + 68.6*x^5 + 785*x^4 + 7213*x^3
+ 50700*x^2 + 8200*x + 435000:
Hurwitz(Lanczos_4,x):
if "=false then print(ok) else print(") fi:
```
Now a series of examples from [, p 559-560, problems 1,2,3, and 6,].
```Henrici_1 := z^3 + mu*z^2 + delta*z + 1:
h(Henrici_1,z,'s','g'):
s:
```
Stable iff and according to [].
```Henrici_2 := z^4 + a*z^3 + b*z^2 + c*z + 1:
h(Henrici_2,z,'s','g'):
s:
```
Stable iff c > 0 and bc - a > 0 and by [].
```ex_1 := 1 + x/1!:
h(ex_1,x):
if "=true then print(ok) else print(") fi:

ex_2 := ex_1 + x^2/2!:
h(ex_2,x):
if "=true then print(ok) else print(") fi:

ex_3 := ex_2 + x^3/3!:
h(ex_3,x):
if "=true then print(ok) else print(") fi:

ex_4 := ex_3 + x^4/4!:
h(ex_4,x):
if "=true then print(ok) else print(") fi:

ex_5 := ex_4 + x^5/5!:
h(ex_5,x):
if "=false then print(ok) else print(") fi:

ex_6 := ex_5 + x^6/6!:
h(ex_6,x):
if "=false then print(ok) else print(") fi:
```
There may be deep implications of the fact that is unstable for n >= 5.
```Bessel_ex := n -> sum( '(n+k)!/(n-k)!/k!*(z/2)^k','k'=0..n):
Bessel_ex(10):
h(",z,'s','g'):
if "=true then print(ok) else print(") fi:

s:
if s=[0,z,3*z,5*z,7*z,9*z,11*z,13*z,15*z,17*z,19*z] then
print(ok)
else
print(")
fi:
```
Should have the pattern .
```p := z^3 + z^2 + 4*z + 30:
h(p,z):
if "=false then print(ok) else print(") fi:
```
Should be false. This example was used to show that the simple necessary criterion of ``all coefficients positive" is not sufficient.

Robert Corless
Wed Feb 28 18:25:56 EST 1996