Visualize Julia Sets using Matlab

function myjulia(Zmax,c,N) % Generate and visualize quadratic Julia Sets % More information about Julia Sets can be found here: % http://en.wikipedia.org/wiki/Julia_set % this code is for the assignment of the "Introduction to Matlab" offered by MITOPENCOURSEWARE % Coded by http://scriptdemo.blogspot.com if (nargin==1)    Ndemo=Zmax; clear Zmax    switch Ndemo    case {1}        myjulia(1,-0.297491+i*0.641051,100);        return;    case {2}        myjulia(0.35,-0.297491+i*0.641051,250);        return;    otherwise       disp('Not defined demo type!')       help myjulia;       return    end elseif (nargin~=3)    help myjulia;    return end % generate the basic matrix NM=500; [Z,tmpy]=meshgrid(linspace(-Zmax,Zmax,NM),zeros(1,NM)); Z=Z+i*Z'; clear tmpy % compute the escape velocity myM=reshape(escapeVelocity(Z(:),c,N),NM,NM); % visualize the results imagesc(atan(0.1*myM)); figurenicer;axis xy; function n=escapeVelocity(z0,c,N) n=z0*0; NLen=length(z0); IndZ=1:length(z0); IndZ=IndZ'; for ni=1:N       IndLT=find(abs(z0)<2);       IndGE=find(abs(z0)>=2);       n(IndZ(IndGE))=ni;       if (length(IndLT)>0)          z0(IndLT)=z0(IndLT).*z0(IndLT)+c;       end       z0(IndGE)=[];       IndZ(IndGE)=[]; end if ~isempty(IndZ)    n(IndZ)=N; end

myjulia(2)

Generate a series of column names in R

#if you want a series of column names, e.g., col1,col2,col3, ..., #you can use: mydf<-data.frame(matrix(ncol=5,nrow=4)) colnames(mydf)<-c("col1","col2","col3","col4","col5") #Well, it does work, but how about for 50 columns? #A loop! Sounds great. Okay, mydf<-data.frame(matrix(ncol=50,nrow=4)) for (n in 1:ncol(mydf)) {       colnames(mydf)[n]<-paste("col",n,sep="") } #But again, it's as urgly as the textbook. Here we offer a much better solution: colnames(mydf)<-paste(rep("col",ncol(mydf)),c(1:ncol(mydf)),sep="") #Smart, eh? At least the nicer looking :) #From http://scriptdemo.blogspot.com

Trim a string in R

# sub-functions # Copyright: http://scriptdemo.blogspot.com mytrim<-function(oristr) {      oristr<-sub("^ +","",oristr)      oristr<-sub(" +$","",oristr)      # or gsub("(^ +)|( +$)","",oristr)      return(oristr) }