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General Computer Science for Engineers CISC 106 Lecture 07

This lecture provides an overview of using Emacs for file editing, plotting data in Matlab, and formatting and displaying output using the fprintf command. Topics include creating and opening files in Emacs, plotting simple graphs, and using fprintf to print formatted output.

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General Computer Science for Engineers CISC 106 Lecture 07

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  1. General Computer Science for EngineersCISC 106Lecture 07 Dr. John Cavazos Computer and Information Sciences 2/25/2009

  2. Lecture Overview • More Emacs • Reading in and editing files • Plotting • Simple Plots • Matlab talks back to you • Using fprintf to display output.

  3. Emacs • Opening a new file • emacs newfile.cpp • Creates a blank file named newfile.cpp for editing • If new file already exists • Emacs newfile.cpp opens file for editing • Save edited file by using GUI or by command Ctrl x followed by Ctrl w.

  4. Emacs • Let’s create a file with two arrays.

  5. Plot • Using the plot command • plot(<array 1>,<array 2>) • where array1 is the x-axis and array2 is the y-axis • NOTE: array1 and array2 must be equal in terms of size of dimensions!

  6. Plot • For example: • x=[1 2 3 4 5]; • y=[10 20 30 40 50]; • plot(x,y)

  7. Plot • Other useful command with plot • xlabel(‘<string>’) – sets the label for the x-axis • ylabel(‘<string>’) – sets the label for the y-axis • grid on – creates a grid • title(‘<string>’) – sets title of the plot

  8. Matlab Output Use the fprintf command print is intuitive, but fprintf? fprintf – formatted print to a file What do files have to do with output to the screen?

  9. Matlab Output Lets look at the syntax count = fprintf(fid, format, A, ...) count – the number of bytes written fid – refers to opened file format – is a format string in between single quotes If fid is set to one or omitted the output goes to the screen.

  10. Matlab Output Example: “There are 5 widgets in inventory” fprintf(‘There are %d widgets in inventory’, widgets); %d acts as a place holder for widget variable at end of command and is known as a conversion character. Conversion characters specify the notation of the output. Note the variable widgets as the second argument.

  11. Matlab Output Use the fprintf command print is intuitive, but fprintf? fprintf – formatted print to a file What do files have to do with output to the screen? Lets look at the syntax count = fprintf(fid, format, A, ...) count – the number of bytes written fid – refers to opened file format – is a format string If fid is set to one or omitted the output goes to the screen.

  12. Matlab Output Example “On average we sell 2.56 widgets every 2 weeks” fprintf(‘On average we sell %f widgets every %d weeks’, widgets_ave, num_weeks); The conversion characters matter %f for fixed point notation 5.6332 %c for a single character ‘s’ %d/%i for signed integers -2354 %s for a string of character “CISC106” Even more conversion characters online in Matlab reference.

  13. Matlab Output Example “Line one Line two” fprintf(“Line one \nLine two”); Is the same as fprintf(“Line one”); fprintf(“\nLine Two”); Escape Characters \n – new line \t – Horizontal tab \b – backspace \\ - Backslash

  14. Matlab Output When MATLAB gives you ugly numbers..... Take pi for example 3.14159265358979323846 Print pi to 4 decimal places fprintf(‘Pi to 4 decimal places %.4f’, pi); 3.1415 Print pi to 7 significant digits fprintf(‘Pi to AT LEAST 7 significant digits %7f’, pi); Significant digits - digits before the decimal point

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