Analysis Methods in Atmospheric and Oceanic Science AOSC 652. Introduction to MATLAB. Week 8, Day Oct 2014

Transcription

1 Analysis Methods in Atmospheric and Oceanic Science 1 AOSC 652 Introduction to MATLAB Week 8, Day 1 20 Oct 2014

2 2 Introduction to MATLAB Matlab stands for MATrix LABoratory. Developed by Matrix based No need to compile Graphical User Interface Good graphics capabilities To run MATLAB,

3 3 Introduction to MATLAB Matlab stands for MATrix LABoratory. Developed by Matrix based No need to compile Graphical User Interface Good graphics capabilities To run MATLAB, at the command line, type matlab

4 4

5 5 Current Directory and file list

6 6 File information

7 7 Command history

8 8 Work space

9 9 Command window

10 10 Reading and writing files: Please copy to your directory: ~tcanty/aosc652/2014/week_08/ascii.m

11 11 Reading and writing files: Please copy to your directory: ~tcanty/aosc652/2014/week_08/ascii.m %write the data file fid = fopen('square_mat.dat', 'wt'); %open the file fprintf(fid, '%s\n', '3,3'); %write the header fprintf(fid, '%s\n', 'column1,column2,column3'); %write the header fprintf(fid, '%s\n', 'This is a square matrix'); %write the header fprintf(fid, '%i\t%i\t%i\n', [1 2 3; 4 5 6; 7 8 9]'); %write data to file fclose(fid); %close file

12 12 Matlab large library of built in mathematical operations accessed under the help menu at the top of your Matlab window at command line type help and then name of the function example: help mean also, try help fprintf

13 13 Reading and writing files: %write the data file fid = fopen('square_mat.dat', 'wt'); %open the file wt = write text file, fid is like the unit number we use in Fortran fprintf(fid, '%s\n', '3,3'); %write the header %s\n = %s prints a string, \n creates a new line fprintf(fid, '%s\n', 'column1,column2,column3'); %write the header fprintf(fid, '%s\n', 'This is a square matrix'); %write the header fprintf(fid, '%i\t%i\t%i\n', [1 2 3; 4 5 6; 7 8 9]'); %write data to file %i\t = %i prints an integer, \t places a tab after each integer fclose(fid); %close file

14 14 Reading and writing files: %read the file back in fid=fopen('square_mat.dat', 'rt'); %open the file title1 = fgetl(fid); %read in the header title2 = fgetl(fid); %read in the header title3 = fgetl(fid); %read in the header [data,count]=fscanf(fid, '%i',[3,3]); %read in data fclose(fid); %close the file

15 15 Reading and writing files: %read the file back in fid=fopen('square_mat.dat', 'rt'); %open the file rt = reads text file title1 = fgetl(fid); %read in the header title2 = fgetl(fid); %read in the header title3 = fgetl(fid); %read in the header [data,count]=fscanf(fid, '%i',[3,3]); %read in data reads a 3x3 integer matrix to data, count is the # of elements fclose(fid); %close the file

16 16 Another way to read data: ~tcanty/aosc652/2014/week_08/load_header_data.m Subroutine is used to read class file format Try reading file we just created: d_nm='/homes/metogra/username/etc '; write in your path here f_nm='square_mat.dat'; [hdr,dats]=load_header_data([d_nm,f_nm]);

17 17 Reading the data into specific arrays: In the command window, type: In the command window type Now type col1 col1' col1=dats(:,1); col2=dats(:,2); col3=dats(:,3);

18 18 Reading the data into specific arrays: In the command window, type: In the command window type Now type col1 col1=dats(:,1); col2=dats(:,2); col3=dats(:,3); col1' What does the ' do?

19 19 How would you take the dot product of two arrays?

20 20 How would you take the dot product of two arrays? In FORTRAN dprod=0. do i=1,3 enddo dmult=col1(i)*col2(i) dprod=dprod+dmult

21 21 How would you take the dot product of two arrays? In MATLAB dprod=col1' *col2

22 22 How would you multiply two arrays? In FORTRAN dimension col4(3) do i=1,3 enddo col4(i)=col1(i)*col2(i)

23 23 How would you multiply two arrays? In MATLAB col4=col1.*col2

24 24 Plotting: Matlab has preset constants such as pi. Let's revisit plotting a sine wave t=[0:0.01:1] ys=sin(2.*pi*t) plot(t,ys) Matlab allows you to interactively add titles from the pull down menus To get rid of the figure type close all

25 25 Plotting 2 curves on the same figure: t=[0:0.01:1] ys1=sin(2.*pi*t) plot(t,ys1,'r-o','linewidth',2) hold on ys2=cos(2.*pi*t) plot(t,ys2,'b-d','markerfacecolor','m') hold off

26 26 Plotting multiple plots on one page figure(1) subplot(2,1,1) t=[0:0.01:1]; ys1=sin(2.*pi*t); plot(t,ys1,'r-o','linewidth',2) ylabel('sine') subplot(2,1,2) ys2=cos(2.*pi*t); plot(t,ys2,'b-d','markerfacecolor','m') ylabel('cos') xlabel('t') hold off

27 27 To plot a plain black solid line: plot(x,y,'k-') To plot a blue line dotted line: plot(x,y,'b:') To plot circles to denote data points: plot(x,y,'o') To plot a green dashed line w/diamonds: plot(x,y,'g--d')