Isn't Ordinary Point Just a Specific Case of Regular Singular Point?

[gikiian]

Consider the ODE y''+P(x)y'+Q(x)y=0.
If \stackrel{limit}{_{x→x_{o}}}P(x) and \stackrel{limit}{_{x→x_{o}}}Q(x) converge, can you call x_{o} a 'regular singular point' besides calling it an 'ordinary point'?

I am saying this because if \stackrel{limit}{_{x→x_{o}}}P(x) and \stackrel{limit}{_{x→x_{o}}}Q(x) converge, then \stackrel{limit}{_{x→x_{o}}}(x-x_{o})P(x) and \stackrel{limit}{_{x→x_{o}}}(x-x_{o})^{2}Q(x) will also converge. And for a second-order linear ODE for which \stackrel{limit}{_{x→x_{o}}}(x-x_{o})P(x) and \stackrel{limit}{_{x→x_{o}}}(x-x_{o})^{2}Q(x) converge, x_{o} is termed as a regular singular point.

 

[lurflurf]

I see what you mean. An ordinary point satisfies the requirements of a regular singular point. For most purposes we want to classify the point (ie ordinary, regular singular, or irregular singular). Thus we would not call a regular singular point an irregular singular point nor an ordinary point a regular singular point.

 

[gikiian]

I totally get that! Thanks :)