Array indices must be positive integers or logical values error when using cell arrays

Question

Aleem Andrew 2020-10-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/611681-array-indices-must-be-positive-integers-or-logical-values-error-when-using-cell-arrays

评论： Ameer Hamza 2020-10-12

The following code is supposed to add a function of x to a function handle f whose coefficients depend on the entries of a cell array a.

a = {{'P',8,0},{'l',-8,0,4},{'P',40,4},{'P',6,-16}}
x = linspace(0,6); 
f = @(x) 0;   
f= f(x) + a{1}{2}*x.^7 
for i = 1:numel(a)
if a{i}{1} == 'P' 
    f = f(x) + a{i}{2}*x;  
end
end

There are no problems in doing this when a polynomial is added outside the for loop but the error message is displayed because of the polynomial a{i}{2}*x which is included in the for loop.

Does anyone have suggestions on how to fix this issue?

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Answer 1

Ameer Hamza 2020-10-12

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https://ww2.mathworks.cn/matlabcentral/answers/611681-array-indices-must-be-positive-integers-or-logical-values-error-when-using-cell-arrays#answer_511831

编辑：Ameer Hamza 2020-10-12

在 MATLAB Online 中打开

You are overwriting the function handle f. Change the name of variable in which you are storing the sum.

a = {{'P',8,0},{'l',-8,0,4},{'P',40,4},{'P',6,-16}}
x = linspace(0,6); 
f = @(x) 0;   
f_ = f(x) + a{1}{2}*x.^7 
for i = 1:numel(a)
if a{i}{1} == 'P' 
    f_ = f(x) + a{i}{2}*x;  
end
end