Is there a sentencing error in the sentencing of a defendant for assault with intent to murder?

Defendant contends there is sentencing error in that the trial court relied on a single factor in aggravation--premeditation (Cal.Rules of Court, rule 421(a)(8))-- which is unsubstantiated by the record. Defendant argues that the record reflects that defendant was suffering from mental problems such that he was unable to " 'maturely and meaningfully reflect upon the gravity of his contemplated act.' [Citations.]" (People v. Horn (1974) 12 Cal.3d 290, 298, 115 Cal.Rptr. 516, 524 P.2d 1300.)