Save variable in workspace but remove from memory?

Question

BOB 2018-9-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/418705-save-variable-in-workspace-but-remove-from-memory

评论： Star Strider 2018-9-13

Hi folks,

I've managed to loop my function to (correctly) determine the distance travelled by each line through the grid cells it intersects. It is as follows:

if true
  for Z = 1:length(ev_longitude)
x1 = -4:10;                                %Grid x-range
A = min(ev_longitude(Z),st_longitude(Z));  %Determine min x coordinate of line
B = max(ev_longitude(Z),st_longitude(Z));  %Determine max x coordiante of line
x = [A B];                                 %x-range of line
y1 = 56:63;                                %Grid y-range
C = min(ev_latitude(Z),st_latitude(Z));    %Determine min y coordinate of line
D = max(ev_latitude(Z),st_latitude(Z));    %Determine max y coordinate of line
y = [C D];                                 %y-range of line
lxmb = @(x,mb) mb(1).*x + mb(2);           %Line equation: y = m*x+b
coefficients = polyfit([A, B], [C, D], 1); %Determine line coefficients
m = coefficients (1);                      %Gradient
b = coefficients (2);                      %y-value intercept
mb = [m b];                                %Matrix of [slope intercept] values
L1 = lxmb(x,mb);                           %Calculate Line #1 = y(x,m,b)
start_of_line = [A C];                     %Start of line 
end_of_line = [B D];                       %End of line
hix = @(y,mb) [(y1-mb(2))./mb(1);  y1];    %Calculate horizontal intercepts
vix = @(x,mb) [x1;  lxmb(x1,mb)];          %Calculate vertical intercepts
hrz = hix(x(1:end),mb)';                   %[X Y] Matrix of horizontal intercepts
vrt = vix(y(1:end),mb)';                   %[X Y] Matrix of vertical intercepts
hvix = [start_of_line; hrz; vrt; end_of_line]; %Concatanated ‘hrz’ and ‘vrt’ arrays
srtd = unique(hvix,'rows');                    %Remove repeats and sort ascending by ‘x’
Longitude_Values = srtd(:,1);
Latitude_Values = srtd(:,2);
i = find((Latitude_Values<=D) & (Latitude_Values>=C));    %Remove values beyond the drawn line
Final_Latitude_Values=Latitude_Values(i);                 %Remove values beyond the drawn line
ii = find((Longitude_Values<=B) & (Longitude_Values>=A)); %Remove values beyond the drawn line
Final_Longitude_Values=Longitude_Values(i);               %Remove values beyond the drawn line
for j = 1:length(Final_Latitude_Values)-1                 %Determine the distance per  each segment
Segment_Distances(j) = sqrt((Final_Longitude_Values(j+1)-Final_Longitude_Values(j))^2 + (Final_Latitude_Values(j+1)-Final_Latitude_Values(j))^2) %euclidean distance in degrees.
end
clearvars -except ev_latitude ev_longitude st_latitude st_longitude
end
end

I want to save the variable Segment_Distances, but unless I clear it from the memory using the clearvars function then it remains in memory and is used incorrectly by the function to calculate the next line's Segment_Distances variable.

I essentially need a way to store the values for Segment_Distances created by the loop, but for the previous values of Segment_Distances to not be incorporated in the next loop.

If anyone can suggest an amendment to this it would be much appreciated.The only data needed is ev_latitude, ev_longitude, st_latitude and st_longitude. These are column vectors of random numbers.

Thanks.

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Answer 1

Star Strider 2018-9-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/418705-save-variable-in-workspace-but-remove-from-memory#answer_336513

在 MATLAB Online 中打开

Since ‘Segment_Distances’ appears to be a scalar, the easiest way would likely be to give it a second subscript:

Segment_Distances(j,k) = ...

then increment ‘k’ in the next loop.

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BOB 2018-9-13

Thanks, I'll go with the subscript option. Could you elaborate on this subscript method? Do you mean as in simply add a loop to the whole script with k as the subscript, and also add this k into the Segment_Distances(j) = ... line as well?

Star Strider 2018-9-13

在 MATLAB Online 中打开

As always, my pleasure.

‘Do you mean as in simply add a loop to the whole script with k as the subscript, and also add this k into the Segment_Distances(j) = ... line as well?’

Yes.

A similar option not involving a 2D matrix for ‘Segment_Distances’:

for j = 1:length(Final_Latitude_Values)-1                 %Determine the distance per  each segment
    Segment_Distances(j) = sqrt((Final_Longitude_Values(j+1)-Final_Longitude_Values(j))^2 + (Final_Latitude_Values(j+1)-Final_Latitude_Values(j))^2) %euclidean distance in degrees.
end
Segment_Distancev(k) = Segment_Distances;