Using the fprintf command to save output to a file.

Transcription

1 Using the fprintf command to save output to a file. In addition to displaying output in the Command Window, the fprintf command can be used for writing the output to a file when it is necessary to save the output. The data that is saved can subsequently be displayed or used in MATLAB and in other applications. Writing output to a file require three steps: a.) Opening a file using the fopen command b.) Writing the output to the open file using the fprintf command c.) Closing the file using the fclose command Step a: Before data can be written to a file, the file must be opened. This is done using the fopen command which creates a new file or opens an existing file. The fopen command has the form. fid=fopen( file_name, permission ) fid is a variable called the file identifier. A scalar is assigned to fid when fopen is executed. The file name, including its extension, is written within single quotes as a string. The permission is a code that tells how the file is opened. Examples of permission codes are r Open file for reading(default) w Open file for writing, if the file already exists its content is deleted. If the file does not exist a new file is created. a Same as w, except that if the file exists the written data is amended to the end of the file. r+ Open file for reading and writing w+ Open file for reading and writing. If the file already exists its content is deleted. If the file doess not exist a new file is created. a+ Same as w+, except that if the file exists the written data is amended to the end of the file. If the permission code is not included then the default is used, r. Step b: Once the file is open, the fprintf command can be used to write output to the file. The fprintf command is used in exactly the same way as it is used to display output in the Command Window, except that the variable fid is inserted inside the command. The fprintf command then has the form:

2 Step c: fprintf(fid, text %-5.2f additional text,variable_name) When the writing of data to the file is complete the file is closed using the fclose command. The fclose command has the form fclose(fid) MATRICES A vector can be created by typing the elements inside square brackets [ ]. Variable_name=[type vector elements] Row vector: to create a row vector type the elements with a space or a comma between the elements inside the square bracket Column vector: to create a column vector type the left square bracket [ and then enter the elements with a semicolon between them, or press the Enter key after each element. Type the right square bracket] after the last element.

3 Two-Dimensional Arrays or Matrices Variable_name=[1 st row elements; 2 nd row elements; 3 rd row elements;.; last row elements]

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5 The zeros, ones and the eye commands: The zeros(m,n), ones(m,n) and eye(n) commands can be used to create matrices that have elements with special values. The zeros(m,n) and the ones(m,n) commands create a matrix with m rows and n columns in which all the elements are the numbers 0 and 1 respectively. The eye(n) command creates a square matrix with n rows and n columns in which the diagonal elements are equal to 1 and the rest of the elements are 0. This matrix is called the identity matrix. The transpose operator: The transpose operator, when applied to a vector, switches a row vector to a column vector. When applied to a matrix switches the rows to columns. The transpose operator is applied by typing a single quote following the variable to be transposed.

6 Array Addressing Elements in an array can be addressed individually or in subgroups. This is a useful when there is a need to redefine only some of the elements when specifics elements are to be used in calculations or when a subgroup of the elements is used to define a new variable.

7 Vectors: Matrix The address of an element in a matrix is its position; defined by the row number and the column number where it is located. For a matrix assigned to the variable ma, ma(k,p) refers to the element in row k and column p. For example ma = Then ma(1,1)=3 and ma(2,3)=10

8 Using a Colon : In Addressing Arrays A colon can be used to address a range of elements in a vector or a matrix. va(:) refers to all the elements of the vector va va(m:n) refers to elements m through n of vector va

9 For a Matrix A(:,n) Refers to the elements in all the rows of column n of the matrix A A(n,:) Refers to the elements in all the columns of row n of the matrix A A(:,m:n) A(m:n,:) Refers to all the elements in all the rows between columns m and n of the matrix A Refers to all the elements in all the columns between rows m and n of the matrix A A(m:n,p:q) Refers to the elements in rows m through n and columns p through q of the matrix A.

10 Creates a matrix B from the 1 st and 3 rd rows, and 1 st, 3 rd and the 5 th through 7 th columns of A Adding Elements to a vector: Elements can be added to an existing vector by assigning values to the new elements. For example, if a vector has 4 elements the vector can be made longer by assigning values to elements 5,6 and so on.

11 MATLAB assigns zeros to the 4 th through 7 th elements Elements can also be added to a vector by appending existing vectors.

12 Adding Elements to a Matrix: Rows and/or columns can be added to an existing matrix by assigning values to the new rows or columns. This must be done carefully since the size of the added rows or columns must fit the new matrix.

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14 MATLAB changes the matrix size to a 4 5 matrix and assigns zeros to the new elements. MATLAB Creates a 3 4 matrix and assigns zeros to all the elements except BG(3,4) Deleting Elements: An element or a range of elements of an existing variable can be deleted by reassigning nothing to these elements. This is done by using square brackets with nothing typed in between them.

15 Built-In Functions for Handling Arrays length(a): Returns the length of a vector A size(a): Returns a row vector [m,n], where m and n are the size of the array reshape(a,m,n): Creates a m by n matrix from the elements of matrix A. diag(v): When v is a vector, creates a square matrix with the elements of v in the diagonal. diag(a): When A is a matrix, creates a vector from the diagonal elements of A.