To define a function named “fun”, the syntax needs to be exactly as typed below.
In[]:=
fun[x_]:=x^2
To define a recursive function, typing the code below will make computing values much faster.
In[]:=
jay[1]:=2
In[]:=
jay[n_]:=jay[n]=2jay[n-1]+4
In[]:=
jay[5]
Out[]=
92
In[]:=
jay[2000]
Out[]=
344439208582276357269849960353304595206695310626608560143292821047729878417711094156997845894951880975533789391696238832034135688258916599427779406849995955617389967435936840002066337444720134614286780970190458734344846390939165091841951078121399061912714989674487196426833888816869934948608492665910998044032506726953375516807138454423742176702804329501287008150119877491566024396708843875283803649951619796986189254381065339575212126479559549754622668301706275761664873350769016117480245871649891748266141276751178046585046359258296163526745827351647875526306586402468528312453896361286554553447088124
In[]:=
jay2[1]:=2
In[]:=
jay2[n_]:=2jay2[n-1]+4
In[]:=
jay2[2000]
$RecursionLimit
:Recursion depth of 1024 exceeded.
Out[]=
4+2TerminatedEvaluation[RecursionLimit]