Singular

The reason:
Singular has a unary -, but no unary +.
Therefore [code]-2x5[/code] is a valid polynomial,
while [code]+2x5[/code] is not.

This issue was fixed by moving the first term of the polynomial to the end of the polynomial.

I'm using Singular via Sage Math, and attempting to generate random polynomials and have Singular calculate their Milnor numbers. The issue arises when I attempt to convert polynomials generated by my algorithm into ones Singular recognizes, some get through successfully while others produce an error.

This is part of a larger piece of code, however this is the error producing step and the error can be replicated outside of the rest of the code. If seeing the rest of the code would be useful, I can provide it.

Working:

[code]
singular('-1s3-8g5-8g5')
singular('-5s5+9v5+9m8')
singular('-4p5+1l9+1l9')
[/code]

Non-Working:

[code]
singular('+4j2-6a7-1e5')
singular('+7f7-7w5+1d8')
[/code]

Error (When a Non-Working Polynomial is Entered):

[code]
sage: R = singular.ring(0,'(j,a,e)','ds')
sage: singular('+4j2-6a7-1e5')
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-37-2b81feafe87b> in <module>()
----> 1 singular('+4j2-6a7-1e5')

/Applications/SageMath-8.6.app/Contents/Resources/sage/local/lib/python2.7/site-packages/sage/interfaces/singular.pyc in __call__(self, x, type)
796 x = str(x)[1:-1]
797
--> 798 return SingularElement(self, type, x, False)
799
800 def _coerce_map_from_(self, S):

/Applications/SageMath-8.6.app/Contents/Resources/sage/local/lib/python2.7/site-packages/sage/interfaces/singular.pyc in __init__(self, parent, type, value, is_name)
1282 except SingularError as x:
1283 self._session_number = -1
-> 1284 raise_(TypeError, TypeError(x), sys.exc_info()[2])
1285 except BaseException:
1286 self._session_number = -1

/Applications/SageMath-8.6.app/Contents/Resources/sage/local/lib/python2.7/site-packages/sage/interfaces/singular.pyc in __init__(self, parent, type, value, is_name)
1277 if not is_name:
1278 try:
-> 1279 self._name = parent._create(value, type)
1280 # Convert SingularError to TypeError for
1281 # coercion to work properly.

/Applications/SageMath-8.6.app/Contents/Resources/sage/local/lib/python2.7/site-packages/sage/interfaces/singular.pyc in _create(self, value, type)
757 """
758 name = self._next_var_name()
--> 759 self.set(type, name, value)
760 return name
761

/Applications/SageMath-8.6.app/Contents/Resources/sage/local/lib/python2.7/site-packages/sage/interfaces/singular.pyc in set(self, type, name, value)
700 cmd += '%s %s=%s;'%(type, name, value)
701 self.__to_clear = []
--> 702 self.eval(cmd)
703
704 def get(self, var):

/Applications/SageMath-8.6.app/Contents/Resources/sage/local/lib/python2.7/site-packages/sage/interfaces/singular.pyc in eval(self, x, allow_semicolon, strip, **kwds)
658 # Singular actually does use that string
659 if s.find("error occurred") != -1 or s.find("Segment fault") != -1:
--> 660 raise SingularError('Singular error:\n%s'%s)
661
662 if get_verbose() > 0:

TypeError: Singular error:
? error occurred in or before STDIN line 68: ``
? last reserved name was `def`
skipping text from `4j2`
[/code]

I am using the Sage Interpreter Interfaces Interface to Singular¶ documentation page.
(I can't link to it due to low karma, sorry!)