MATLAB: Could any one please advise me on what is wrong with this code

code problems

function classGrades = convertGrades NamesAndGrades (1:5,:)

L = 20; % size of M, NamesAndGrades

c = 11; % last column of the submatrix (of course c < L)

% create the submatrix (NamesAndGrades)

M = rand(L);

% extract the desired submatrix

grades = M(:,2:c);

end

Best Answer

Hi,

so, many problems :

first line : what is the name of your function ? convertGrades, NamesAndGrades ? and in this line (1:5,:) has nothing to do here.

last line : grades = M(:,2:c); the output of your function is classGrades which is not defined in your code, i guess you need classGrades = M(:,2:c); ?

so depends on what you want to do, but here is function which works :

function classGrades = convertGrades 
L = 20; 
c = 11; 
M = rand(L);
classGrades = M(:,2:c);
end

Related Solutions

MATLAB: C. Extract the sub-matrix containing all the rows but only columns 2 through 11 and name this matrix grades (to make this work on any size matrix, do not hard-code the 11, but rather use end or size).

Hi,

I'm not sure I understand your question. You should provide a concise title and a possibly detailed statement of the problem, not the other way round. Anyway, if I get it right, you have a matrix (say, M) and you want the submatrix containing all the rows and colums 2 trough some c. This matrix should be called grades. This is pretty simple.

 L = 20;     % size of M, for practical purposes
 c = 11;     % last column of the submatrix (of course c < L)
 % create the submatrix (for practical purposes, you have it from your source)
 M = rand(L);
 % extract the desired submatrix
 grades = M(:,2:c);

MATLAB: How to index and replace

totalGrade is already the index (values from one to five) that can be used directly into letters, therefore you do not need find or the equivalence operation, and I also simplified your concatenating characters into one string:

 letters = 'FDCBA';
 letterGrades = letters(totalGrades)

This simply follows exactly what the instructions state: "make the final letter grades ... by using totalGrades... to index into letters". The instructions do not tell you to use find, or equivalence operators.

In fact all of your code uses unnecessary find operations, and very inefficient loops. Loops are not the point of this homework. The very first line states that the point is to think about using MATLAB "in terms of matrices and vectors because that is how MATLAB organizes data". You are still thinking in terms of loops, which are slow, ugly, and are definitely not thinking about data in terms of matrices and vectors.

For example, this slow find and ugly loop:

 curvedGrades5 = find(curvedGrades > 5)
 for i = curvedGrades5
   curvedGrades(i) = 5;
 end

should be just one line using logical indexing:

 curvedGrades(curvedGrades>5) = 5;

If you want to learn how to use MATLAB efficiently then you need to revise your work, and especially learn about logical indexing.

Best Answer

Related Solutions

MATLAB: C. Extract the sub-matrix containing all the rows but only columns 2 through 11 and name this matrix grades (to make this work on any size matrix, do not hard-code the 11, but rather use end or size).

MATLAB: How to index and replace

Related Question