Programming with SCILAB (pdf)

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C = ! 57. 74. 49. 52. 61. 54. ! ! 95. 104. 102. 83. 101. 119. ! ! 58. 112. 88. 76. 94. 122. ! -->D = matrixmult(B,A) !--error 9999 matrixmult - incompatible matrices A and B at line 10 of function matrixmult called by : D = matrixmult(B,A) Of course, matrix multiplication in SCILAB is readily available by using the multiplication sign (*), e.g., -->C = A*B C = ! 57. 74. 49. 52. 61. 54. ! ! 95. 104. 102. 83. 101. 119. ! ! 58. 112. 88. 76. 94. 122. ! -->D = B*A !--error 10 inconsistent multiplication Reading a table from a file The first example presented in this section uses the command file to open a file for reading, and the function read for reading a matrix out of a file. This application is useful when reading a table into SCILAB. Suppose that the table consists of the following entries, and is stored in the file c:\table1.dat: 2.35 5.42 6.28 3.17 5.23 3.19 3.87 3.21 5.18 6.32 1.34 5.17 8.23 7.28 1.34 3.21 3.22 3.23 3.24 3.25 8.17 4.52 8.78 2.31 1.23 9.18 5.69 3.45 2.25 0.76 The following function reads the table out of file c:\table1.dat and separates the 5 columns into a number of variables x1, x2, x3, x4, x5: function [x1,x2,x3,x4,x5] = readtable() //|---------------------------------------| //| This is an interactive function that | //| requests from the user the name of a | //| file containing a table and reads the | //| table out of the file. The table has | //| exactly 5 columns. | //|---------------------------------------| printf("Reading a table from a file\n") printf("===========================\n") printf(" ") filname = input("Enter filename between quotes:\n") u = file('open',filname,'old') //open input file 20
Table = read(u,-1,5) [n m] = size(Table) printf(" ") printf("There are %d columns in the table",m) for j = 1:m execstr('x'+string(j)+' = Table(:,j) ') end close(u) //close input file The file command in function readtable uses three arguments, the first being the option ‘open’ to indicate that a file is being opened. The second argument is the file name, and the third is a qualifier indicating that the file already exists (required for input files). Also, the left-hand side of this statement is the variable u which will be given an integer value by SCILAB. The variable u represents the logical input-output unit assigned to the file being opened. Function readtable uses the command read with the second argument being -1 which allows for not knowing the number of rows in the matrix to be read. With this argument set to -1, SCILAB will read all rows in the matrix. The number of columns, however, needs to be known (This is not too difficult to find out since we have access to the input file -- a text file -- through a text editor program, e.g., PFE). Notice the line execstr('x'+string(j)+' = Table(:,j) ') in function readtable. This line puts together a string that becomes the argument of function execstr. For example, if j=1, the argument becomes ‘x1 = Table(:,1)’. Function execstr (execute string) then translate the resulting string into a SCILAB command. Thus, for this example, it will be equivalent to writing: x1 = Table(:,1) As shown in function readtable, it is always a good idea to insert a close statement to ensure that the file is closed and available for access from other programs. Function readtable assumes that all the files to be read have only 5 columns. The columns are returned into variables x1, x2, x3, x4, x5. Here is an example of application of function readtable. User response is shown in bold face. -->[x1,x2,x3,x4,x5] = readtable() Reading a table from a file =========================== Enter filename between quotes: -->'c:\table1.dat' There are 5 columns in the table x5 = ! 5.23 ! ! 6.32 ! ! 1.34 ! ! 3.25 ! ! 1.23 ! ! .76 ! x4 = ! 3.17 ! ! 5.18 ! ! 7.28 ! ! 3.24 ! ! 2.31 ! ! 2.25 ! 21
Page 1 and 2: Programming with SCILAB By Gilberto
Page 3 and 4: If the inputs to the function will
Page 5 and 6: A function can return a matrix, for
Page 7 and 8: class = "The flow is turbulent " en
Page 9 and 10: The following is an application of
Page 11 and 12: An example of application of this f
Page 13 and 14: ===================================
Page 15 and 16: 2.0 1.8 1.6 1.4 1.2 1.0 0 2 4 6 8 1
Page 17 and 18: A single evaluation of function sum
Page 19: or, --> surf(x,y,z’) 9.7 0.0 -9.7
Page 23 and 24: -->myTableFile() Printing to a file
Page 25: elow apply only to the references i

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