Conditional equations with cell arrays.

I have two cell arrays as an example. One cell array has positive values, one array has negative values. The cell array with negative values also has zeros.

y = {0 0 0 -179.4 0 -179.3 -178.3 -173.2 -178.9 -179.6}

x = {173.5 169.4 177.5 172.8 169.8 166.6 179.2 178.0 169.7 174.5}

The values represent maximum degrees of movement. The y array is the maximum negative component (if there was one) and the x array is the minimum positive component. 180 (or zero) equals an upright torso and no range of motion. I need to find out the total range of motion. For example the total range of motion between the first values in each array is 6.5 (180 - 173.5). If there is a maximum negative value as with the fourth movement, the range of motion would be 7.8 ((180 - abs(y{4}) + (180 - x{4})). I want to write a statement that performs one equation if there is a zero (180 - 173.5) and another if there is not a zero ((180 - abs(y{4}) + (180 - x{4})) and creates a new cell array of values {1:10}. I have tried the below for loop with if else statement without success. If I put the value of the cell in the place of i, the correct value is displayed. Otherwise for i, I get a single value that is 5.4 and I don't know where it comes from. If I write the loop with ROM{i} then there is an error.

for i = 1:length(y);  
if y{i} == 0 
     ROM = (180 - x{i});
elseif y{i} < 0
     ROM = (180 - abs(y{i})) + (180 - x{i});
else 
end

end

Help appreciated.

Answer 1

[Star Strider]

In one line with ‘logical indexing’:

y = {0	0	 0	-179.4	0	-179.3	-178.3	-173.2	-178.9	-179.6};
x = {173.5	169.4	177.5	172.8	169.8	166.6	179.2	178.0	169.7	174.5};

fcn = @(x,y) (180-[x{:}]).*([y{:}]==0) + ((180 - abs([y{:}])) + (180 - [x{:}])).*([y{:}]<0);

ROM = fcn(x,y)

producing:

ROM =

  Columns 1 through 7

          6.5         10.6          2.5          7.8         10.2         14.1          2.5

  Columns 8 through 10

          8.8         11.4          5.9

To use the loop, index ‘ROM’. The ‘logical indexing’ approach is faster and more efficient.

[Nickolai Martonick]

Thank you! Could you tell me what the purpose of the @ symbol?

[Star Strider]

As always, my pleasure!

The ‘@’ creates a function handle, here specifically denoting an anonymous function.

See the documentation on Anonymous Fucntions and What Is a Function Handle? for details.