MAT-File Format - SERC
MAT-File Format - SERC MAT-File Format - SERC
1 MAT-File FormatFor example, if a data element represents a 2-by-3-by-2 MATLAB array, theDimensions Array subelement would contain three values: 2, 3, and 2.Note To calculate the number of dimensions in an array, divide the valuestored in the Number of Bytes field in the Dimensions Array subelement tagby 4, the number of bytes in the data type (miINT32) used in the subelement.Array Name SubelementThis subelement specifies the name assigned to the array, as an array ofsigned, 8-bit values (miINT8). This subelement is common to all array types.Real Part (pr) SubelementThis subelement contains the numeric data in the MATLAB array. If the arraycontains complex numbers (the complex bit in the Array Flags is set), this isthe real part of the number.The data type of the values can be any of the numeric data types listed inTable 1-1, MAT-File Data Types, on page 1-9.For character data that is not Unicode encoded, the Data Type part of the Tagfield should be set to miUINT16.Imaginary Part (pi) SubelementThis subelement contains the imaginary part of the numeric data in theMATLAB array. This subelement is only present if one or more of the numericvalues in the MATLAB array is a complex number (if the complex bit is set inArray Flags). The data type of the values can be any of the numeric data typeslisted in Table 1-1, MAT-File Data Types, on page 1-9.Note When reading a MAT-file, check the value of the Data Type field in thetag of Real Part and Imaginary Part subelements to identify the data typeused to store data. Also note that MATLAB reads and writes these values incolumn-major order.1-18
Level 5 MATLAB Array Data Element FormatsAutomatic Compression of Numeric DataMATLAB stores the numeric data in an array in double precision format. WhenMATLAB writes a numeric (or sparse) array to a MAT-file, it uses the smallestpossible data type to store the data, both the real and imaginary parts.For example, if MATLAB determines that the data stored in double precisionformat can actually be stored in an 8-bit format, it will use an 8-bit data typeto store it in a MAT-file. Note, however, that if any of the numeric values in thearray requires a 64-bit representation, MATLAB stores all of the data in a64-bit data type. See “Compressed Data Element” on page 1-21 for an example.When you create a MAT-file, compressing data is optional.Note When MATLAB uses a smaller data type to store data in a MAT-file,the value of the Class field in the Array Flags subelement identifies theoriginal MATLAB data type.Examples of Numeric Array Data ElementsThis section uses examples to illustrate both the compressed anduncompressed numeric array data element formats.Uncompressed Data Element. Figure 1-7 shows how this 2-by-2 numeric array,my_array, is represented in a MAT-file.my_array = [ 1.1+1.1i 2 ; 3 4 ]my_array =1.1000 + 1.1000i 2.00003.0000 4.00001-19
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1 <strong>MAT</strong>-<strong>File</strong> <strong>Format</strong>For example, if a data element represents a 2-by-3-by-2 <strong>MAT</strong>LAB array, theDimensions Array subelement would contain three values: 2, 3, and 2.Note To calculate the number of dimensions in an array, divide the valuestored in the Number of Bytes field in the Dimensions Array subelement tagby 4, the number of bytes in the data type (miINT32) used in the subelement.Array Name SubelementThis subelement specifies the name assigned to the array, as an array ofsigned, 8-bit values (miINT8). This subelement is common to all array types.Real Part (pr) SubelementThis subelement contains the numeric data in the <strong>MAT</strong>LAB array. If the arraycontains complex numbers (the complex bit in the Array Flags is set), this isthe real part of the number.The data type of the values can be any of the numeric data types listed inTable 1-1, <strong>MAT</strong>-<strong>File</strong> Data Types, on page 1-9.For character data that is not Unicode encoded, the Data Type part of the Tagfield should be set to miUINT16.Imaginary Part (pi) SubelementThis subelement contains the imaginary part of the numeric data in the<strong>MAT</strong>LAB array. This subelement is only present if one or more of the numericvalues in the <strong>MAT</strong>LAB array is a complex number (if the complex bit is set inArray Flags). The data type of the values can be any of the numeric data typeslisted in Table 1-1, <strong>MAT</strong>-<strong>File</strong> Data Types, on page 1-9.Note When reading a <strong>MAT</strong>-file, check the value of the Data Type field in thetag of Real Part and Imaginary Part subelements to identify the data typeused to store data. Also note that <strong>MAT</strong>LAB reads and writes these values incolumn-major order.1-18
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