MATLAB to XDL Plotting Guide

Overview

MATLAB’s plotting syntax is significantly different from XDL’s, and many MATLAB plotting features are not supported by the transpiler. This guide shows how to translate MATLAB plotting code to XDL.

The Challenge

Complex MATLAB plotting code like this will not work:

x = linspace(0, 2*pi, 100);
y1 = sin(x);
y2 = cos(x);
figure;
plot(x, y1, 'b-');
hold on;
plot(x, y2, 'r--*');
xlabel('x-axis');
ylabel('y-axis');
title('Sine and Cosine');
legend('Sine', 'Cosine');
hold off;

Why it doesn’t work:

  • ❌ linspace() not implemented
  • ❌ figure, hold not supported
  • ❌ xlabel, ylabel separate commands not supported
  • ❌ legend not supported
  • ❌ Line styles 'b-', 'r--*' not parsed
  • ❌ Array operations sin(x) where x is array

The Solution: Write in XDL

Here’s the equivalent XDL code that does work:

; Create x values from 0 to 2*PI
n_points = 100
x = FINDGEN(n_points) * 2.0 * !PI / (n_points - 1)

; Calculate sine and cosine
y_sin = SIN(x)
y_cos = COS(x)

; Plot with labels
PLOT, x, y_sin, title='Sine and Cosine Functions', xtitle='X (radians)', ytitle='Y values'

Key Differences

1. Array Generation

MATLAB:

x = linspace(0, 2*pi, 100);

XDL:

x = FINDGEN(100) * 2.0 * !PI / 99.0

2. Constants

MATLAB:

x = 2 * pi;

XDL:

x = 2 * !PI

Available: !PI, !E, !DTOR, !RTOD

3. Plotting Syntax

MATLAB:

plot(x, y);
xlabel('X Axis');
ylabel('Y Axis');
title('My Plot');

XDL:

PLOT, x, y, title='My Plot', xtitle='X Axis', ytitle='Y Axis'

4. Multiple Plots

MATLAB:

figure;
plot(x, y1);
hold on;
plot(x, y2);
hold off;

XDL (Current Limitation):

; Currently, XDL generates one plot per PLOT command
; Multiple curves on same plot not yet supported
PLOT, x, y_sin, title='Sine Function', xtitle='X', ytitle='Sin(X)'
; This would overwrite the previous plot:
; PLOT, x, y_cos, title='Cosine Function', xtitle='X', ytitle='Cos(X)'

Practical Examples

Example 1: Simple Sine Plot

MATLAB (.m file):

% Won't work - uses linspace and array operations
x = linspace(0, 6.28, 50);
y = sin(x);
plot(x, y);
title('Sine Wave');

XDL (.xdl file) - Works:

x = FINDGEN(50) * 6.28 / 49.0
y = SIN(x)
PLOT, x, y, title='Sine Wave', xtitle='X', ytitle='sin(x)'

Example 2: Exponential Function

MATLAB (.m file):

% This actually works! (simple scalar math)
x = 2.0;
y = exp(x);
disp(y);

Output: 7.389...

This works because it uses only:

  • Scalar variables
  • Supported functions (exp)
  • disp for output

Example 3: What You Can Do in MATLAB Files

For simple calculations, .m files work:

% examples/matlab/simple_calc.m
a = 5;
b = 10;
c = sqrt(a^2 + b^2);
disp('Hypotenuse:');
disp(c);

This transpiles and runs successfully!

Best Practices

Use MATLAB Files For

  • ✅ Simple scalar calculations
  • ✅ Testing individual math functions
  • ✅ Basic demonstrations
  • ✅ Learning/prototyping

Use XDL Files For

  • ✅ Array operations
  • ✅ Plotting
  • ✅ Loops
  • ✅ Complex programs
  • ✅ Production code

Complete Working Example

See these examples in the examples/ directory:

MATLAB (Limited):

  • examples/matlab/01_simple_math.m ✅
  • examples/matlab/02_trigonometry.m ✅
  • examples/matlab/03_simple_operations.m ✅
  • examples/matlab/04_simple_plot.m ✅ (demonstrates limitations)

XDL (Full Featured):

  • examples/xdl/03_plotting_basics.xdl ✅
  • examples/xdl/04_trigonometry.xdl ✅
  • examples/xdl/06_sine_cosine_plot.xdl ✅

Migration Path

If you have MATLAB code:

  1. Try It: Run simple .m files through the transpiler
  2. Check Errors: Note what features aren’t supported
  3. Rewrite in XDL: For arrays, plots, and complex features
  4. Use XDL Syntax: Take advantage of full XDL capabilities

Future Work

The transpiler may eventually support:

  • linspace() function
  • Array literal syntax
  • Better loop support
  • Plot style hints (converted to XDL equivalents)

For now, use native XDL for anything beyond basic scalar math.

Quick Reference

MATLAB XDL Equivalent Status
linspace(0, 10, 100) FINDGEN(100) * 10.0 / 99.0 Workaround
pi !PI Use system var
plot(x,y) PLOT, x, y Different syntax
[1,2,3] FINDGEN(3) + 1 No direct equiv
sin(array) SIN(array) XDL only
disp(x) PRINT, x Transpiled ✅
log(x) ALOG(x) Transpiled ✅

See Also

  • docs/MATLAB_LIMITATIONS.md - Complete limitations list
  • docs/MATLAB_SUPPORT.md - Supported features
  • examples/README.md - All examples documentation