#lesson 17 Ocober 2007
#All R-commands that you need for this lesson

#You can directly paste the commands/ this file into the R-window to try out the commands
#Questions: see help function ?command, or ask me tlaepple@awi-bremerhaven.de

############# this letter is used for comments

#?function   shows the help for a function
?sin

#There is no definition needed for simple (scalar) variables
#but instead of =, <- is used
#just assign name<-value

a<-1

#Print the number on the screen: 
a #prints only on the console
print(a) #prints always

#simple algebraic calculations
a<-2*3
a<-a/2
print(a) # and print again


#some vector / array functions
#vectors / arrays normally need to be defined that R can distinguish it
#from a scalar.

y<-vector() #Produces an empty vector... 

#the size of vectors in R is dynamic... I can now assign y[1]...
#Assign elements of the vector [i], Vectors index are starting with 1

y[1]<-1
y[2]<-2
print(y)
print(y[1])

#very often vectors filled with equidistant values are needed
x<-1:10   #x = vector (1,2,3,4,5,6,7,8,9,10)
print(x)
x<-(1:100)/5  # (0.2,0.4,0.6 ..........)
print(x)



#2D matrix
#matrix(values_to_fill_the_matrix,dimension1,dimension2)
data<-matrix(0,10,10) #creates a matrix with the dimensions 10x10, filled with 0's
data<-matrix(1:100,10,10) #creates a matrix with the dimensions 10x10, filled with the values 1:100 (columnwise)
#Accessing a matrix
data[4,4]     # Element 4,4 of the matrix
data[1:4,1:4] #the upper left 4x4 part of the matrix
data[1,]      #First row of the matrix
data[,1]      #First column of the matrix



#Control structures:
#for loop: for (variable in array) { }
for (i in 1:100) 
{	
	print(i)
}



#plotting function

#plot(y), plot y against equidistant steps
y<-1:100
plot(y)

#plot(x,y), plot y against x
x<-(1:100)*5
plot(x,y)  #note the changes in the x-axis



#2D plotting functions
#colour Contour + Colorbar:
#filled.contour(x_coordinates,y_coordinates,data[x,y],zlim=c(minvalue,maxvalue))
#contour lines:
#contour(x_coordinates,y_coordinates,data[x,y)

#Example
data<-matrix(1:100,10,10) #Create a 10x10 matrix filled with 1..100

filled.contour(data) #plot the data, automatic colorrange
filled.contour(data,zlim=c(0,20)) #Set the colorrange to 0..20
contour(data)  #Contour plot of the data





# some examples for adding labels etc. to plots:

#further parameters that can be used in plotting commands.
#type = "l" : as line type
#col = "color": plotting color
#ylim = c(minval,maxval):Set the limits of the y-axis
#main = "title": sets the title


plot(x,y,col="red",main="example",type="l",ylim=c(1,70))

#overplotting: line(x,y) or line(y) is the same as the plot command but plots
#a line on an already existing plot whereas plot is starting a new plot

z<-x^2 / 100
plot(x,y,col="red",main="example",type="l",ylim=c(1,70))
lines(x,z,col="blue")


#defining a function
multiply <- function(x,y)
{
	return(x*y)
}

print(multiply(3,4))