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<body bgcolor = "#FFFFCC"><basefont face = "Arial"> |
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<h1>SVM: Support Vector Machines</h1> |
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<h1>Training Initialization Dialog</h1> |
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<h2> Parameter Information</h2> |
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<hr size = 10> |
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<h2>Classification Input</h2> |
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The SVM training process requires the supplied expression data and |
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an additional initial presumptive classification which indicates |
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which elements are initially presumed to have a relationship. |
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Two options are provided for selecting members of the initial classification. |
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<h3>Use SVM Classification Editor</h3> |
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This option causes an editor application to be launched in order to |
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allow a flexible tool for finding and marking elements to be positive members |
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of the initial classification. This classification can be save as an |
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SVC file for later recovery of these initial settings. |
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<h3>Use Classification File</h3> |
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This allow the loading of an initial classification from an |
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existing SVC file. |
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<h2>Kernel Matrix Construction</h2> |
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One can select to construct a polynomial or a radial kernal matrix. |
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<br> |
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<h2>Polynomial Kernel Function Parameters</h2> |
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The polynomial option is the default and three parameters are used to define |
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the kernel construction. |
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<h3>Constant</h3> |
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An additive constant. (c) |
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<h3>Coefficient</h3> |
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A multiplicative constant. (w) |
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<h3>Power</h3> |
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A power factor. (p) |
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<br> |
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<h3>Polynomial Kernel Function</h3> |
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K(i,j) = [w*(Dist(i,j)+c)]<sup>p</sup> |
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<br><br> |
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<h2>Radial Basis Function Parameters</h2> |
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The Radial Basis checkbox is used to select to use this type of Kernal generating function. |
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<h3>Width Factor</h3> |
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Radial width factor (w, see in below formula). |
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<br> |
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<h3>Radial Basis Kernel Function</h3> |
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K(x,y) = e<sup>( - (||x - y||<sup><font size = 2>^2</font></sup>)/(2w<sup><font size = 2>^2</font></sup>))</sup> |
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<br> |
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<h2>Training Parameters</h2> |
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<h3>Diagonal Factor</h3> |
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Constant added to the main diagonal of the kernel matrix. |
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Adding this factor to the main diagonal of the kernel is required to force |
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the matrix to be 'positive definite'. The definition of a positive definite |
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matrix is best reviewed in books devoted to linear algebra but this |
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state is achieved by selecting a constant of sufficient magnitude. |
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<br><br> |
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This positive definite state of the kernel matrix is required for the SVM algorithm to |
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yeild meaningful results. Testing values starting at 1.0 and increasing |
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may be required to find an appropriate value. If the value is too low all |
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elements will be partitioned in the negative class. For a range of values |
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for this factor a stable set of elements may be classified as positive. |
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At very high values there is a tendancy to force all positive expamples |
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to be in the positive class regardless of their similarity of expression. |
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<h3>Threshold</h3> |
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This value is used as a stopping criteria for the weight optimization phase of training. |
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Optimizing the weights produced during training is an iterative process which converges |
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on an optimal set of weights to separate the positive and negative examples. |
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This threshold dictates how stable the weights must be before the optimization process |
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is terminated. Selection of a threshold that is very low could cause the |
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optimization process to take an extremely long time and yet yeild similar results to those where |
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a higher threshold value was used which terminated the process earlier. |
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<h3>Constraints</h3> |
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This check box selects to apply limits to weights produced during training. |
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<h3>Positive Constraint</h3> |
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The upper limit to produced weights. |
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<h3>Negative Constraint</h3> |
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The lower limit to produced weights. |
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</basefont> |
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</body> |
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</html> |
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