creating table in matlab of elliptic curve points

I get the points of elliptic curve and then when I try to convert that 1D array into 2D and try to make a table some error appears need help here is an example of code

if true
  % code
end
disp('y^2 = x^3 + 5376x + 2438 mod 123457')
a=0:123456
left_side = mod(a.^2,123457);
right_side = mod(a.^3+5376*a+2438,123457);
points = [];
for i = 1:length(right_side)
  I = find(left_side == right_side(i));
  for j=1:length(I)
      points = [points;a(i),a(I(j))];
  end
end
plot(points(:,1),points(:,2),'ro')
set(gca,'XTick',0:1:123456)
set(gca,'YTick',0:1:123456)
grid on;
Z=reshape(points,[256,482])

[Steven Lord]

What is the full text of the error message you receive when you run that code, and on which line does the error occur? Show us all the text displayed in red (and if you receive any warnings in orange, show us the full text of those warning messages as well.)

[Muhammad Sohail Abid]

this text appears

if true
  % code
end
Error using reshape
To RESHAPE the number of elements must not change.
Error in ECPoint (line 16)
Z=reshape(points,[256,482])

Answer 1

[Walter Roberson]

You are asking to reshape a 123387 by 2 array into a 256 x 482 array. The number of elements in the array is not divisible by 256 or 482 -- it is just slightly less than 482 * 256 * 2

[Walter Roberson]

Some values for a do not match anything; others match 2 things. And three of the a values match one thing -- and in each case that one thing is 0

[Muhammad Sohail Abid]

yes I know we will padup or append last 5 entries with zero to make it divisible by 256 and 482 in last column the remaining entries will be filled with zeros but I don't know how to do it need help

[Walter Roberson]

pad_needed = 256 - (mod(size(points,1) - 1, 256) + 1);
if pad_needed > 0
  points(end+pad_needed,:) = 0;
end

points will now be a multiple of 256 rows: it should work out as 256 * 482 rows, so at this point you could consider

Z = reshape(points, [256, 482]);

However, this will fail, because you have forgotten about the second column. You would not have 256 x 482 array elements: you would have 256 x 482 x 2 array elements.

[Muhammad Sohail Abid]

if true
  % code
end
Error using reshape
To RESHAPE the number of elements must not change.
Error in EC (line 20)
Z = reshape(points, [256, 482]);

[Muhammad Sohail Abid]

this error arises can you please help me to fix this reshaping

[Walter Roberson]

Sorry, I cannot seem to find words that make it sufficiently clear to you that you have 256 times 482 times 2 data points that you are trying to reshape into a 256 times 482 times 1 array.

Imagine that you have an array

A B
C D
E F
G H
I J
K L

and you ask to reshape() it to be a 3 x 2 array. Now, the number of rows you have is 6, and 6 is 3 x 2, so you think you should be able to do the reshape. But you cannot do that, because the 3 x 2 array you would end up would have only 6 total entries, but the 6 x 2 array that you start with has 12 total entries. You cannot make a 3 x 2 array out of the 6 x 2 array except by throwing away half of the data.