MATLAB: Error: Array indices must be positive integers or logical values.

array

Here is my code:

clc;clear;
t=[0:0.5:60];
h(t)=2.03*t.^2-0.0013*t.^4+0.000034*t.^4.751;
plot(t, h(t));
xlabel('Time');
ylabel('Height(m)');

But I get this error when I try to evaluate:

Array indices must be positive integers or logical values.

I need 100 values from 0 to 60 for my graph.

Thank you!

Best Answer

Please read https://www.mathworks.com/matlabcentral/answers/395816-why-do-i-get-array-indices-must-be-positive-integers-or-logical-values-error-when-using-angle-fu#comment_882605

Related Solutions

MATLAB: Array indices must be positive integers or logical values.

The error text pretty much explains why you are getting an error.

"Array indices must be positive integers or logical values"

Matlab arrays are indexed with array indices that start with 1 for the first index in the array.

You are trying to index using t= 0:142.27 which starts at zero (which is not a valid array index in Matlab). Note also that, since you have not provided a step size for constructing this vector, the last element of the vector will be 142 (not 142.27) because Matlab assumes a step size of one if you don't tell it otherwise.

You probably need to define your t vector with a step size (for example t = [0:0.01:142.27]) and then, using the fact that Matlab operates on vectors as well as scalars, you can get your answer for the whole vector at once with this:

h = (30^(5/2)-(5*sqrt(2)*9.8/2)*t).^(2/5) ;

Note that there is not a (t) on the left hand side. You correctly had the .^ instead of ^ to get element-wise operations but the left hand side can accept the entire vector result without the index.

I hope this helps.

MATLAB: How to add equation to function

Note: the following can be done trivially without a loop by vectorisation.

t = 0:2:100;
h=zeros(size(t));
for k=1:numel(t);
    h(k) = rocket(t(k))
    if h(k)>=0
       disp(h(k));      
    end 
end
function h = rocket(t)
         h = (60+(2.13*(t^2))-(0.0013*(t^4))+(0.000034*(t^4.751)));
end

Without loop:

t = 0:2:100;
h = rocket(t); 
fprintf('h >= 0:%f\n',h(h>=0))
function h = rocket(t) 
         h = (60+(2.13*(t.^2))-(0.0013*(t.^4))+(0.000034*(t.^4.751)));
end

Best Answer

Related Solutions

MATLAB: Array indices must be positive integers or logical values.

MATLAB: How to add equation to function

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