how to access values inside a matrix or array in a 'for' loop??

Question

Manoj Murali 2012-2-4

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https://ww2.mathworks.cn/matlabcentral/answers/28052-how-to-access-values-inside-a-matrix-or-array-in-a-for-loop

编辑： Jan 2013-9-30

采纳的回答： Andrei Bobrov

在 MATLAB Online 中打开

suppose i hav two matrices or arrays named m and n.They have 4 values each like this.

m=56 67 89 103

n=45 78 92 71

now i need to plot 4 dots on an image using the above corresponding m and n values as (x,y) coordinates.So how to do it.i have written a code for this.But it is showing error.Any one plz hlp me fix this.

for i = 0:3

    x=m.i;
    y=n.i;
    h=imread('C:\Users\Manoj\Desktop\sorry.jpg');
    imshow(h)
    hold on;
    plot(x,y,'r.','MarkerSize',15)
end

I dont know how to access the values inside the m and n.So i doubt the error is in the steps m.i and n.i.

The output of the program must be an figure window with four dots plotted at the four (x,y) points.Where x,y must take values from m and n respectively.Help me plz..

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Answer 1

Andrei Bobrov 2012-2-4

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https://ww2.mathworks.cn/matlabcentral/answers/28052-how-to-access-values-inside-a-matrix-or-array-in-a-for-loop#answer_36331

在 MATLAB Online 中打开

h=imread('C:\Users\Manoj\Desktop\sorry.jpg');
imshow(h)
hold on;
plot(m,n,'r.','MarkerSize',15)

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Manoj Murali 2012-2-4

thanq sir..

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Answer 2

the cyclist 2012-2-4

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https://ww2.mathworks.cn/matlabcentral/answers/28052-how-to-access-values-inside-a-matrix-or-array-in-a-for-loop#answer_36332

在 MATLAB Online 中打开

This

m.i

is not how to access the i th element of m. Use

 x=m(i)
 y=n(i)

instead. Also, though, you shouldn't have to use a for loop at all. You can do this with a vector, and just do

plot(m,n,'r.','MarkerSize',15)

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Manoj Murali 2012-2-4

sir,as u told i used this after modifying m.i to m(i)...but my output showed only one dot on the image at the last values of m and n.I need all the 4 points to b plotted sir..cud u help me..??

for i = 1:4

x=m(i);

y=n(i);

h=imread('C:\Users\Manoj\Desktop\sorry.jpg');

imshow(h)

hold on;

plot(x,y,'r.','MarkerSize',15)

end

Manoj Murali 2012-2-4

While the other method worked,that doing it with out the for loop.But

to gain some insight on how to implement this using the for loop am asking u..plz dont mind sir..help me to plot all the 4 points on the image instead of only the last 4th point being plottted as i told u in previous comment....

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