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1 ---
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2 layout: page
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3 title: Examples
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4 permalink: /examples/
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5 menu: true
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6 ---
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8 ### Using Octave
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10 First, follow the [installation guide]({{ site.baseurl/install/ }}) to install Octave on your system. Then, launch the interactive prompt by typing `octave` in a terminal or by clicking the icon in the programs menu. For further guidance, see the manual page on [Running Octave]({{site.docs_url}}Running-Octave.html).
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12 ### Language Basics
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14 Click the headings below to see a manual page related to each topic
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15 {: .panel}
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17 ###### [Variable Assignment]({{site.docs_url}}Variables.html)
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19 Assign values to variables with `=` (Note: assignment is <a href="#" data-reveal-id="assignmentModal">pass-by-value</a>)
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21 ###### [Comments]({{site.docs_url}}Comments.html)
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23 `%` starts a comment block that continues to the end of the line.
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25 ###### [Evaluation]({{site.docs_url}}Simple-Examples.html)
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27 The output of every command is printed to the console unless terminated with `;`. The `disp()` command can be used to print output anywhere. Use `exit` to quit the console.
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29 {% highlight matlab %}
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30 t = 99 + 1 % prints 't = 100'
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31 t = 99 + 1; % nothing is printed
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32 disp(t);
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33 100
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34 {% endhighlight %}
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36 ###### [Math]({{site.docs_url}}Arithmetic.html)
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38 Many mathematical operators are available in addition to the standard arithmetic.
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39 Operations are floating-point.
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40 {% highlight matlab %}
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41 x = 3/4*pi;
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42 y = sin(x)
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43 0.70711
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44 {% endhighlight %}
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45
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46 ###### [Matrices]({{site.docs_url}}Matrices.html)
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47
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48 Arrays in Octave are called matrices.
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49 One-dimensional matrices are referred to as vectors.
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50 Use `space` or `,` to separate elements and `;` to start a new row.
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51
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52 {% highlight matlab %}
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53 rowVec = [8 6 4]
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54 8 6 4
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55 columnVec = [8; 6; 4]
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56 8
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57 6
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58 4
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59 mat = [8 6 4; 2 0 -2]
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60 8 6 4
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61 2 0 -2
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62 size(mat)
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63 2 3
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64 length(rowVec)
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65 3
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66 {% endhighlight %}
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67
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68 ###### [Linear Algebra]({{site.docs_url}}Linear-Algebra.html)
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70 Many common linear algebra operations are simple to program using Octave's matrix syntax.
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71
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72 {% highlight matlab %}
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73 columnVec * rowVec
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74 64 48 32
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75 48 36 24
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76 32 24 16
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77 rowVec * columnVec
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78 116
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79 columnVec'
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80 8 6 4
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81 {% endhighlight %}
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82
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83 ###### [Accessing Elements]({{site.docs_url}}Index-Expressions.html)
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84
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85 Octave is 1-indexed. Matrix elements are accessed as `matrix(rowNum, columnNum)`.
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86
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87 {% highlight matlab %}
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88 mat(2,3)
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89 -2
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90 {% endhighlight %}
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91
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92 ###### [Iteration]({{site.docs_url}}Statements.html)
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93
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94 Octave supports `for` and `while` loops, as well as other control flow structures.
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95
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96 {% highlight matlab %}
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97 x = zeros(50,1);
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98 for i=1:2:100 % iterate from 1 to 100 with step size 2
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99 x(i) = i^2;
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100 end
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101
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102 y = zeros(50,1);
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103 k = 1;
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104 step = 2;
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105 while k<=(100-step)
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106 y(i) = k^2;
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107 k = k + step;
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108 end
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109 {% endhighlight %}
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110
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111 ###### [Vectorization]({{site.docs_url}}Vectorization-and-Faster-Code-Execution.html)
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112
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113 For-loops can often be replaced or simplified using vector syntax.
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114 The operators `*`,`/`,`^`,`%` all support element-wise operations using `.`.
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115 Many other functions operate element-wise by default (`sin`,`+`,`-`, etc.).
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116
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117 {% highlight matlab %}
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118 i = 1:2:100; % create a 50-element array
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119 x = i.^2; % each element is squared
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120 y = x + 9; % add 9 to each element
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121 z = y./i; % divide each element in y by the corresponding value in i
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122 w = sin(i/10); % take the sine of each element รท 10
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123 {% endhighlight %}
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124
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125 ###### [Plotting]({{site.docs_url}}Two_002dDimensional-Plots.html)
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126
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127 `plot` can be called with vector arguments to create 2D line and scatter plots.
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128
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129 {% highlight matlab %}
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130 plot(w,i/10);
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131 title('w = sin(i/10)';
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132 xlabel('i รท 10');
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133 ylabel('w');
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134 {% endhighlight %}
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135
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136 <img src="{{site.baseurl}}/img/sinePlot.png" alt="sine plot" style="height: 20rem; width: auto;" />
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137
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138
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139 ###### [Strings]({{site.docs_url}}Strings.html)
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140
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141 Strings are simply arrays of characters.
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142 Strings can be composed using `printf`-style formatting with `sprintf` and `fprintf`.
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143 {% highlight matlab %}
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144 firstString = 'hello world';
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145 secondString = '!';
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146 [firstString,secondString]
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147 hello world!
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148 fprintf('%s %.10f \n', 'The number is:', 10)
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149 The number is: 10.0000000000
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150 {% endhighlight %}
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151
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152 ###### [If-else]({{site.docs_url}}The-if-Statement.html)
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153
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154 Conditional statements can be used to create branching logic in your code.
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155
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156 {% highlight matlab %}
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157 % Print 'Foo' if divisible by 7,
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158 % 'Fizz' if divisible by 3,
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159 % 'Buzz' if divisible by 5,
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160 % 'FizzBuzz' if divisible by 3 and 5
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161 for (i = 1:1:100)
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162 outputString = '';
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163 if (rem(i,3) == 0) % rem is the remainder function
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164 outputString = [outputString, 'Fizz'];
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165 end
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166 if (rem(i,5) == 0)
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167 outputString = [outputString, 'Buzz'];
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168 elseif (rem(i,7) == 0)
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169 outputString = 'Foo';
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170 else
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171 outputString = outputString;
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172 end
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173 fprintf('i=%g: %s \n',i,outputString);
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174 end
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175 {% endhighlight %}
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176
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177 {% highlight text %}
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178 ...
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179 i=12: Fizz
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180 i=13:
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181 i=14: Foo
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182 i=15: FizzBuzz
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183 ...
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184 {% endhighlight %}
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185
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186 ###### [Help]({{site.docs_url}}Simple-Examples.html#Help-and-Documentation)
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187
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188 The `help` and `doc` commands can be invoked at the Octave prompt to print documentation for any function.
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189
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190 {% highlight matlab %}
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191 help plot
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192 doc plot
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193 {% endhighlight %}
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194
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195 ###### [Packages]({{site.docs_url}}Packages.html)
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196
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197 Community-developed packages can be added from the
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198 [Octave Forge](http://octave.sourceforge.net/index.html)
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199 to extend the functionality of Octave's core library.
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200 (Matlab users: Forge packages act similarly to Matlab's toolboxes.)
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201 The `pkg` command is used to manage these packages.
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202 For example, to use the image processing library from the Forge, use:
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203
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204 {% highlight matlab %}
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205 pkg install -forge image % install package
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206 pkg load image % load new functions into workspace
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207 {% endhighlight %}
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208
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209 <div id="assignmentModal" class="reveal-modal tiny" data-reveal aria-hidden="true" role="dialog">
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210 {% highlight matlab %}
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211 a = 1
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212 b = a
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213 b = 2
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214 a == b % returns 0 (false)
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215 {% endhighlight %}
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216 <a class="close-reveal-modal" aria-label="Close">&#215;</a>
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217 </div>