9.2 Dcfinit,ioii of the Foiirier Transforiri 197 Its inagnitiiclc \ X ( J J ) is called the rnngrirfudc spectrum The pltnsr , S ~ J p p ( w ) is usually c'upr d bp the phase p ( l w ) At the hegiiirriiig it is CO that oiic writes X ( j , i ) arid ~ ( J L ; ) ,ii11tl not S ( d ) and p(w) T'rrr argurnci j u s t a conveiition which mcans that a one-diinrnrionnl cwniplrs tiinct,ion in the an mrnbcr plarre on t,hc iiir;iginar>r axib is b&ig defined it could illso bc clefined as X(d) on thc real axis, and there arc actinally rcvcral boolis tliat tlu this - tlie clcpeiiclenc*y OII iil is im iigpd Tlic sciise of tlie ju! ronvrntion becoiiies irurnediai (sly c lcar if a relationship between Fourier and lap lac^ tr ansforrris i s made (Sectioii 9.3) For the Fourici [xansforiii?the abbreviated corrrspoudency form (9.3) will br iised CT7c use [lie same relit transfornir, for example, symbol is rrol, strict n-mt hcthe J,apl