"I'm trying to add an 'if' statement to analyze each result, but Matlab is 'ignoring' the condition and not performing the addition."

"I'm trying to add an 'if' statement to analyze each result, but Matlab is 'ignoring' the condition and not performing the addition."

I need that when some value of c (not all) is less than 0, d becomes rad2deg(theta) + 180, when any of the values of c is greater than or equal to 0, d becomes rad2deg(theta)

"The values of c are attached."

I think I'm not managing to explain my problem, I'll try again:

theta = acos(UV ./ Uv);

c = Y(:,2); where Y(:,2) is generated by ode45, meaning there are several values (a total of 547).

I need to check the values of "c." When the value of "c" is < 0, the value of "d" is d = rad2deg(theta) + 180; when not, d = rad2deg(theta).

So, for each value analyzed in "c," a value of "d" is calculated (if <0, d = rad2deg(theta) + 180; if not, d = rad2deg(theta)), meaning, in the end, I will have 547 values of "d" based on the rules above.

Thank you very much for your attention.

[T,Y] = ode45(@myprog,tSpan,s,options);
.
.
.
c = Y(:,2);
if c < 0
    d = rad2deg(theta) + 180;
else
    d = rad2deg(tetha);
end

[Walter Roberson]

Is theta a scalar or a vector? Is it calculated from c? Is it possibly the same as c ?

[Daniel santiago Umaña]

"The values of c are attached."

I need to take these values, and if they are less than 0, d = rad2deg(theta) + 180, if they are greater than zero, d = rad2deg(theta)

Answer 1

[the cyclist]

Is c a vector? If so, then all elements of c would have to be less than zero, to enter the if condition. This is explained in the documentation.

[Walter Roberson]

The second output of ode45 is guaranteed to have at least three rows (unless there are perhaps some strange combinations of circumstances.) Just maybe if there was an event function that always signalled termination you might be able to get it down to two rows.

[Daniel santiago Umaña]

"The values of c are attached."

I need to take these values, and if they are less than 0, d = rad2deg(theta) + 180, if they are greater than zero, d = rad2deg(theta)

Answer 2

[Torsten]

c is a vector. Do you want d to be rad2deg(theta) + 180 if all elements of the vector c are < 0 ? Then your code is correct. Otherwise you have to loop over the elements of c:

for i = 1:size(c,1)
    if c(i) < 0 
        ...
    else
        ...
    end
end

[Daniel santiago Umaña]

I need that when some value of c (not all) is less than 0, d becomes rad2deg(theta) + 180, when any of the values of c is greater than or equal to 0, d becomes rad2deg(theta)

[Walter Roberson]

theta = pi/3;
c = [-1 -1/2];

if nnz(c<0) < numel(c)   %some value but not all
    d = rad2deg(theta) + 180;
end
if any(c >= 0)
    d = rad2deg(theta);
end

d

Unrecognized function or variable 'd'.

The output d is undefined for the case where all values are c are strictly less than 0.;

[Walter Roberson]

theta = pi/3;
c = [-1 1/2];

if nnz(c<0) < numel(c)   %some value but not all
    d = rad2deg(theta) + 180;
end
if any(c >= 0)
    d = rad2deg(theta);
end

d

d = 60.0000

Some but not all c were less than 0, so the +180 case applies. But some c are greater than 0, so the non-180 applies. Both conditions apply the same time, so the output d needs to be simultaneously the +180 case and also not the +180 case. This is a logical problem.

[Daniel santiago Umaña]

"The values of c are attached."

I need to take these values, and if they are less than 0, d = rad2deg(theta) + 180, if they are greater than zero, d = rad2deg(theta)

[Walter Roberson]

load matlab
theta = pi/3;

d_valid_count = 0;
if all(c<0)   %some value but not all
    d = rad2deg(theta) + 180;
    d_valid_count = d_valid_count + 1;
end
if all(c >= 0)
    d = rad2deg(theta);
    d_valid_count = d_valid_count + 1;
end
if d_valid_count > 0
    fprintf('%d rule(s) activated; according to last used rule, d is:\n', d_valid_count)
    d 
else
    %for example if all c < 0 then the rule does not define the output
    error('your rules did not match the situation')
end

your rules did not match the situation

[Walter Roberson]

load matlab
theta = pi/3;

d_valid_count = 0;
if any(c<0)   %some value but not all
    d = rad2deg(theta) + 180;
    d_valid_count = d_valid_count + 1;
end
if any(c >= 0)
    d = rad2deg(theta);
    d_valid_count = d_valid_count + 1;
end
if d_valid_count > 0
    fprintf('%d rule(s) activated; according to last used rule, d is:\n', d_valid_count)
    d 
else
    %for example if all c < 0 then the rule does not define the output
    error('your rules did not match the situation')
end

2 rule(s) activated; according to last used rule, d is:

d = 60.0000

[Walter Roberson]

I would suggest to you that your rules have not been properly defined. I would suggest to you that your theta is an array the same size as c is, and that you want each theta element to be converted according to its corresponding c value.

[Daniel santiago Umaña]

I think I'm not managing to explain my problem, I'll try again:

theta = acos(UV ./ Uv);

c = Y(:,2); where Y(:,2) is generated by ode45, meaning there are several values (a total of 547).

I need to check the values of "c." When the value of "c" is < 0, the value of "d" is d = rad2deg(theta) + 180; when not, d = rad2deg(theta).

So, for each value analyzed in "c," a value of "d" is calculated (if <0, d = rad2deg(theta) + 180; if not, d = rad2deg(theta)), meaning, in the end, I will have 547 values of "d" based on the rules above.

Thank you very much for your attention.

[Torsten]

We don't know the size of the array "theta", but most probably you mean

for i = 1:size(c,1)
    if c(i) < 0 
        d(i) = rad2deg(theta(i)) + 180
    else
        d(i) = rad2deg(theta(i))
    end
end

or shorter

d = rad2deg(theta);
d(c<0) = d(c<0) + 180;

[Daniel santiago Umaña]

Thank you very much, this is exactly what I needed! Thanks!