MATLAB: Inequality problem

inequality

Hi…. Does the following inequality work on Matlab:

for col=1:1:num_cols

    if (0.00>(real_qn1(col))<0.25)
        real_c(col)=(1/sqrt(2));
    else if (0.25>(real_qn1(col))<0.50)
            real_c(col)=(-1/sqrt(2));
        else if (0.50>(real_qn1(col))<0.75)
                real_c(col)=(-sqrt(2));
            else if (0.75>(real_qn1(col))<1.00)
                    real_c(col)=(sqrt(2));
                end
            end
        end
    end
end
I tried it.. But it's giving me inverted results..

Thank you

Best Answer

You have to split them up... instead of:

A < X < B

you have to do:

(A < X) && (X < B)

Incidentally, make sure you are using good logic. At your first if you have:

0.00 > X < 0.25

which is the same(*) as saying:

(X < 0.0) && (X < 0.25)

The second part is redundant, because if X is less than 0.0 it is also less than 0.25

(*) By saying "same" I mean the way you would interpret the statement. Matlab executes those two statements very differently.

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MATLAB: Making a surface in 3D space with sample some irregular points

You could use the code below as a starting point. First, get rid of the commas and read in your data as follows:

p=[0.010 0.053 0.020
...
0.025 0.032 0.005];

Then find the convex hull:

K = convhull(p);

Finally, plot the surface:

trisurf(K,p(:,1),p(:,2),p(:,3))

The matrix K provides three indices in each row that define a triangle (each index refers to the appropriate row of coordinates in your data matrix). If it doesn't correspond to the surface you want, you'll probably need to create K manually.

MATLAB: TEXTSCAN Reading After a specified term(or a row) and writing matrix.

This file poses two problems when using TEXTSCAN.

The number of headerlines is not known beforehand.
The number of columns is not known beforehand.

There are many alternative ways to read this file. (If speed is important one might use fread.) One solution with textscan is shown below. The approach is

read the complete file and store each row as one string
find the row with the keyword, "END", which indicates the end of the header and delete the header
determine the number of columns and the number of rows
convert the cell array of strings to a string array, which can be read by textscan. textscan reads by columns and thus the array need to be permuted. textscan swallows the newline characters and thus we need to add new ones.
generate a format string and read the string array
convert the cell array, which textscan returns, to a numerical array.

I've added a variant based on fread. The basic approach is the same.

read the complete file to a character column vector and permute it to a row
find the position of the keyword, END. To be sure to find the right END: search for [new_line, any_space, END, any_space, new_line]
catch the data part of the character row
extract the first row of data and count the columns
create a format string and read the character row with textscan

The textscan variant takes care of the space_characters, but requires code to "unpack" cell arrays.

With the fread variant there is no need to "unpack" cell arrays, but code is needed to take care of the space_characters. Especially, char(13), must not be overlooked.

--- The End ---

function    M = Answer( )       
    fid  = fopen( 'cssm.txt', 'r' );
    cac  = textscan( fid, '%s', 'Delimiter', '\n' );
    sts  = fclose( fid );
    ixe  = find( strncmp( 'END', cac{1}, 3 ), 1, 'last' );
    buf  = cac{1}( ixe+1:end, : ); 
    ncol = numel( regexp( buf{1}, ' +', 'split' ) );
    nrow = size( buf, 1 );
    str  = cat( 1, permute(char(buf),[2,1]), repmat(sprintf('\n'),1,nrow) );
    frmt = repmat( '%f', 1, ncol );
    cac  = textscan( str, frmt );
    M    = [ cac{:} ];
end

and the variant based on fread

function    M = Answer( )    
    fid  = fopen( 'cssm.txt', 'r' );
    str  = permute( fread( fid, '*char' ), [2,1] );
    sts  = fclose( fid );
    ixe  = regexp( str, '\n\s*END\s*\n', 'end' );
    buf  = str( ixe+1 : end );
    ix2  = regexp( buf, '\d\s*\n', 'start', 'once' );
    ncol = numel( regexp( strtrim( buf(1:ix2) ), ' +', 'split' ) );
    frmt = repmat( '%f', 1, ncol );
    cac  = textscan( buf, frmt );
    M    = [ cac{:} ];
end

Best Answer

Related Solutions

MATLAB: Making a surface in 3D space with sample some irregular points

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