How can this Python code be written in Matlab? I'm trying to write a Matlab script that will allow two Stepper motors to scan in a Raster pattern but all I can find is this Python script. How the 'for' loop be replicated in Matlab?

from pylab import *

# define some grids
xgrid = arange(20, 31) 
ygrid = arange(10, 16)

xscan = []
yscan = []

for i, yi in enumerate(ygrid):
    xscan.append(xgrid[::(-1)**i]) # reverse when i is odd
    yscan.append(ones_like(xgrid) * yi)   

# squeeze lists together to vectors
xscan = concatenate(xscan)
yscan = concatenate(yscan)

# quick plot
plot(xscan, yscan, '.-')
axis([19, 31, 9, 16])
show()

[Rik]

I have never worked with Python, so I can't translate this to Matlab. If you explain your original problem, people might be able to help you.

(This looks like it is relatively basic Python. Have you tried looking up the documentation for these functions?)

[David Sweeney]

Hi, I'm trying to write a MATLAB code that will allow two stepper motors to move an ultrasonic scanner in a raster pattern via an arduino microcontroller. The only part I am having trouble with is MATLAB code.

[Rik]

That is not the Matlab part of your problem. What is it you want to do? It looks like you want to plot some dotted line path. Is that the case? If so, what constraints are there?

[David Sweeney]

What I'm trying to do in this code is start at some point within the grid say (0,0) then move a fixed amount of steps in the x direction until say (5,0) then take a step in the y direction to (5,1) then step backwards in the x direction to say (0,1). This will mimic the raster pattern I am trying to build. I've attached some Matlab code but it doesn't work the same as the above python code.

clear all
%initialise input parameters
ymin=0;
ystep=1;
ymax=1;
xmin=0;
xstep=1;
xmax=5;
x1=0;

for y = ymin:ystep:ymax

      for x0=xmin:xstep:xmax

          fprintf(' coordinates X,Y(%d,%d)  \n' , x0, y);

      end
      if x0==xmax
              for x1 = xmax:-xstep:xmin

          fprintf('coordinates X,Y(%d,%d)  \n' , x1, y);
              end
      end
  end

Answer 1

[Rik]

There is a Cody question that asked you to produce a matrix like the one below

X=[1 2 3;
  6 5 4;
  7 8 9];

My solution was a variation of the code below

x_num_steps=round((xmax-xmin)/xstep)+1;
y_num_steps=round((xmax-xmin)/xstep)+1;
sort_order=reshape(1:(x_num_steps*y_num_steps),x_num_steps,y_num_steps)';
sort_order(2:2:end,1:end)=sort_order(2:2:end,end:-1:1);

You can use this matrix to sort your coordinate grid (which you can generate with meshgrid). (You will need to transpose it to get the correct order.) [X,Y]=meshgrid(linspace(xmin,xmax,x_num_steps),linspace(ymin,ymax,y_num_steps)); %vectorize and sort X and Y sort_order=sort_order(:); X=X(:);Y=Y(:); X=X(sort_order);Y=Y(sort_order);

So, here all of the code:

%initialize variables
ymin=0;
ystep=1;
ymax=1;
xmin=0;
xstep=1;
xmax=5;

%calculate the number of steps in each direction (i.e. grid lines)
%this also catches the case where the gap isn't an integer multiple of the step size
x_num_steps=round((xmax-xmin)/xstep)+1;
y_num_steps=round((xmax-xmin)/xstep)+1;
%create a matrix with 1:total number of steps (grid points)
sort_order=reshape(1:(x_num_steps*y_num_steps),x_num_steps,y_num_steps)';
sort_order(2:2:end,1:end)=sort_order(2:2:end,end:-1:1);
sort_order=sort_order';
%sort_order contains the order in which we should go through the X and Y matrices
[X,Y]=meshgrid(linspace(xmin,xmax,x_num_steps),linspace(ymin,ymax,y_num_steps));
%vectorize and sort X and Y
sort_order=sort_order(:);
X=X(:);Y=Y(:);
X=X(sort_order);Y=Y(sort_order);
%plot the line and zoom out a bit to show the path
plot(X,Y,'--')
axis([xmin-xstep xmax+xstep ymin-ystep ymax+ystep])

[David Sweeney]

Hi, thanks for clearing that up! That's helped a lot!

[David Sweeney]

Hi, could you add some comments to your code please? I'm having trouble deciphering it! I intend to use one stepper motor to move in the x direction and the other in the y direction, hence I need to know what variable I should be putting inside the 'move()' function. Thanks so much!

[Rik]

See edit

Answer 2

[Guillaume]

What I'm trying to do in this code is start at some point within the grid say (0,0) then move a fixed amount of steps in the x direction until say (5,0) then take a step in the y direction to (5,1) then step backwards in the x direction to say (0,1).

What is the difficulty with that? And why use a loop for that (let alone two)?

xmin = 0; xmax = 5; xstep = 1;
ymin = 0; ymax = 1; ystep = 1;

%step 1: go from xmin to xmax, in xstep. y stays at ymin:
x = xmin:xstep:xmax;
y = repelem(xmin, numel(x));
xy = [x; y];

%step 2: go from ymin to max, in ystep. x stays where it is:
y = ymin+ystep:ystep:ystep;  
x = repelem(xy(1, end), numel(y));
xy = [xy, [x; y]];

%step 3: go back to xmin. y stays constant
x = xmax-xstep:-xstep:xmin;
y = repelem(xy(2, end), numel(x));
xy = [xy, [x; y]]

[David Sweeney]

Hi, thanks for taking the time to answer this! I was asked to use a loop to do this but it was getting too complicated with 'if' and 'for' loops. Any ideas how you would implement a loop along the same lines of what I have attached? Thanks again!

clear all
%initialise input parameters
ymin=0;
ystep=1;
ymax=1;
xmin=0;
xstep=1;
xmax=5;
x1=0;
x=0:5;

for y = ymin:ystep:ymax

      for x0=xmin:xstep:xmax

          fprintf(' coordinates X,Y(%d,%d)  \n' , x0, y);

      end
      if x0==xmax
              for x1 = xmax:-xstep:xmin

          fprintf('coordinates X,Y(%d,%d)  \n' , x1, y);
              end
      end
  end

[Rik]

You shouldn't try to do it with a loop. If you want to, you can still print either my solution or the solution by Guillaume, but why would you?

If you want a plot, you just use plot(X,Y,'--') with my solution, or a similar call with this solution.

[David Sweeney]

Hi Guillaume, using your code would there be a way to finish the x routine (xmin to xmax in xstep increments) carry out the y routine (do a ystep) then do a -x routine (xmax to xmin) then do another y routine and so on until the full pattern is developed? when I change the ymax setting from 1 to 2 for example the results don't seem correct. I've attached the output when ymax is 10:

coordinates X,Y(0,0)  
 coordinates X,Y(1,0)  
 coordinates X,Y(2,0)  
 coordinates X,Y(3,0)  
 coordinates X,Y(4,0)  
 coordinates X,Y(5,0)  
 coordinates X,Y(6,0)  
 coordinates X,Y(7,0)  
 coordinates X,Y(8,0)  
 coordinates X,Y(9,0)  
 coordinates X,Y(10,0)  Around this point it seems to do a y step after each xstep instead of a ystep after each x routine
 coordinates X,Y(10,1)  
 coordinates X,Y(10,2)  
 coordinates X,Y(10,3)  
 coordinates X,Y(10,4)  
 coordinates X,Y(10,5)  
 coordinates X,Y(10,6)  
 coordinates X,Y(10,7)  
 coordinates X,Y(10,8)  
 coordinates X,Y(10,9)  
 coordinates X,Y(10,10)  
 coordinates X,Y(9,10)  
 coordinates X,Y(8,10)  
 coordinates X,Y(7,10)  
 coordinates X,Y(6,10)  
 coordinates X,Y(5,10)  
 coordinates X,Y(4,10)  
 coordinates X,Y(3,10)  
 coordinates X,Y(2,10)  
 coordinates X,Y(1,10)  
 coordinates X,Y(0,10)

Answer 3

[Andrei Bobrov]

[ii,jj] = ndgrid(20:30,10:15);
ii(:,2:2:end) = flip(ii(:,2:2:end));
plot(ii(:),jj(:));
axis([19, 31, 9, 16]);