what is the meaning of y(i,j) and x(i,j) in the code below? [closed]

[poster]

in this code below i am simulating the flow over the sphinx of ibiza and the pyramd i am trying to make the code in python but i am not understanding what is the meaning of y(i,j) and x(i,j) in the iteration loop i tried to make a for loop for x and y but it seems that i am a straight streamline can someone help?

 close all;

    clear;

    clc;



    disp('Part b')



    %% 



    V_inf=25; %uniform flow

    C_s=2; %circulation of vortices around sphynx

    C_p=3.25; %circulation of vortices around pyramid



    %% coordinates of vortices



    S_1=[13.966 0.2359];

    S_2=[13.7464 0.7247];

    S_3=[14.0353 1.062];

    S_4=[14.3243 1.2803];

    S_5=[14.0657 1.2803];

    S_6=[13.8827 1.8382];

    S_7=[13.67 2.2322];

    S_8=[13.1772 2.6921];

    S_9=[12.2791 2.8433];

    S_10=[11.6264 2.8433];

    S_11=[11.3163 2.4508];

    S_12=[11.3127 1.9264];

    S_13=[11.2179 1.4682];

    S_14=[11.3474 1.0634];

    S_15=[11.3127 0.5757];

    S_16=[11.1604 0.1907];



    P_1=[7.9398 0.5117];

    P_2=[7.4442 0.9823];

    P_3=[6.9758 1.4271];

    P_4=[6.5624 1.8197];

    P_5=[6.1236 2.2364];

    P_6=[5.7148 2.6248];

    P_7=[4.9071 1.9994];

    P_8=[4.1875 1.4424];

    P_9=[3.3127 0.7654];

    P_10=[2.5914 0.2072];



    %% iteration loop



    [x,y]=meshgrid(0:0.1:20,0:0.05:10);



    for i=1:length(x)

        for j=1:length(y)

            PSI(i,j)=-V_inf*y(i,j)-(C_s/2*pi).*log(sqrt((x(i,j)-S_1(1)).^2+(y(i,j)-S_1(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_1(1)).^2+(y(i,j)+S_1(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_2(1)).^2+(y(i,j)-S_2(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_2(1)).^2+(y(i,j)+S_2(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_3(1)).^2+(y(i,j)-S_3(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_3(1)).^2+(y(i,j)+S_3(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_4(1)).^2+(y(i,j)-S_4(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_4(1)).^2+(y(i,j)+S_4(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_5(1)).^2+(y(i,j)-S_5(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_5(1)).^2+(y(i,j)+S_5(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_6(1)).^2+(y(i,j)-S_6(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_6(1)).^2+(y(i,j)+S_6(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_7(1)).^2+(y(i,j)-S_7(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_7(1)).^2+(y(i,j)+S_7(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_8(1)).^2+(y(i,j)-S_8(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_8(1)).^2+(y(i,j)+S_8(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_9(1)).^2+(y(i,j)-S_9(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_9(1)).^2+(y(i,j)+S_9(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_10(1)).^2+(y(i,j)-S_10(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_10(1)).^2+(y(i,j)+S_10(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_11(1)).^2+(y(i,j)-S_11(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_11(1)).^2+(y(i,j)+S_11(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_12(1)).^2+(y(i,j)-S_12(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_12(1)).^2+(y(i,j)+S_12(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_1(1)).^2+(y(i,j)-P_1(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_1(1)).^2+(y(i,j)+P_1(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_2(1)).^2+(y(i,j)-P_2(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_2(1)).^2+(y(i,j)+P_2(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_3(1)).^2+(y(i,j)-P_3(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_3(1)).^2+(y(i,j)+P_3(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_4(1)).^2+(y(i,j)-P_4(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_4(1)).^2+(y(i,j)+P_4(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_5(1)).^2+(y(i,j)-P_5(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_5(1)).^2+(y(i,j)+P_5(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_6(1)).^2+(y(i,j)-P_6(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_6(1)).^2+(y(i,j)+P_6(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_7(1)).^2+(y(i,j)-P_7(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_7(1)).^2+(y(i,j)+P_7(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_8(1)).^2+(y(i,j)-P_8(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_8(1)).^2+(y(i,j)+P_8(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_9(1)).^2+(y(i,j)-P_9(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_9(1)).^2+(y(i,j)+P_9(2)).^2))-(C_p/2*pi).*log(sqrt((x(i,j)-P_10(1)).^2+(y(i,j)-P_10(2)).^2))+(C_p/2*pi).*log(sqrt((x(i,j)-P_10(1)).^2+(y(i,j)+P_10(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_13(1)).^2+(y(i,j)-S_13(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_13(1)).^2+(y(i,j)+S_13(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_14(1)).^2+(y(i,j)-S_14(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_14(1)).^2+(y(i,j)+S_14(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_15(1)).^2+(y(i,j)-S_15(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_15(1)).^2+(y(i,j)+S_15(2)).^2))-(C_s/2*pi).*log(sqrt((x(i,j)-S_16(1)).^2+(y(i,j)-S_16(2)).^2))+(C_s/2*pi).*log(sqrt((x(i,j)-S_16(1)).^2+(y(i,j)+S_16(2)).^2));

        end 

    end



    %% figures



    [v,u] = gradient(PSI,1,1); 





    figure(1)

    quiver(x(1:8:size(x,1),1:8:size(x,1)),y(1:8:size(y,1),1:8:size(y,1)),u(1:8:size(u,1),1:8:size(u,1)),-v(1:8:size(-v,1),1:8:size(-v,1)),3);

    hold on 

    contour(x,y,PSI,100);



    figure(2)

    contour(x,y,PSI,100);

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