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<p>This implementation is a special case of the class of isometric log-ratio transformations.</p>
<pre><span class='fu'>ilr</span>(<span class='no'>x</span>)
<span class='fu'>invilr</span>(<span class='no'>x</span>)</pre>
<h2>Arguments</h2>
<dl class="dl-horizontal">
<dt>x</dt>
<dd>
A numeric vector. Naturally, the forward transformation is only sensible for
vectors with all elements being greater than zero.
</dd>
</dl>
<div class="Value">
<h2>Value</h2>
<p>The result of the forward or backward transformation. The returned components always
sum to 1 for the case of the inverse log-ratio transformation.</p>
</div>
<div class="References">
<h2>References</h2>
<p>Peter Filzmoser, Karel Hron (2008) Outlier Detection for Compositional Data Using Robust Methods. Math Geosci 40 233-248</p>
</div>
<div class="See also">
<h2>See also</h2>
<p>Another implementation can be found in R package <code>robCompositions</code>.</p>
</div>
<h2 id="examples">Examples</h2>
<pre class="examples"><div class='input'><span class='co'># Order matters</span>
<span class='fu'>ilr</span>(<span class='fu'>c</span>(<span class='fl'>0.1</span>, <span class='fl'>1</span>, <span class='fl'>10</span>))</div><div class='output co'>#> [1] -1.628174 -2.820079
#> </div><div class='input'><span class='fu'>ilr</span>(<span class='fu'>c</span>(<span class='fl'>10</span>, <span class='fl'>1</span>, <span class='fl'>0.1</span>))</div><div class='output co'>#> [1] 1.628174 2.820079
#> </div><div class='input'><span class='co'># Equal entries give ilr transformations with zeros as elements</span>
<span class='fu'>ilr</span>(<span class='fu'>c</span>(<span class='fl'>3</span>, <span class='fl'>3</span>, <span class='fl'>3</span>))</div><div class='output co'>#> [1] 0 0
#> </div><div class='input'><span class='co'># Almost equal entries give small numbers</span>
<span class='fu'>ilr</span>(<span class='fu'>c</span>(<span class='fl'>0.3</span>, <span class='fl'>0.4</span>, <span class='fl'>0.3</span>))</div><div class='output co'>#> [1] -0.2034219 0.1174457
#> </div><div class='input'><span class='co'># Only the ratio between the numbers counts, not their sum</span>
<span class='fu'>invilr</span>(<span class='fu'>ilr</span>(<span class='fu'>c</span>(<span class='fl'>0.7</span>, <span class='fl'>0.29</span>, <span class='fl'>0.01</span>)))</div><div class='output co'>#> [1] 0.70 0.29 0.01
#> </div><div class='input'><span class='fu'>invilr</span>(<span class='fu'>ilr</span>(<span class='fl'>2.1</span> * <span class='fu'>c</span>(<span class='fl'>0.7</span>, <span class='fl'>0.29</span>, <span class='fl'>0.01</span>)))</div><div class='output co'>#> [1] 0.70 0.29 0.01
#> </div><div class='input'><span class='co'># Inverse transformation of larger numbers gives unequal elements</span>
<span class='fu'>invilr</span>(-<span class='fl'>10</span>)</div><div class='output co'>#> [1] 7.213536e-07 9.999993e-01
#> </div><div class='input'><span class='fu'>invilr</span>(<span class='fu'>c</span>(-<span class='fl'>10</span>, <span class='fl'>0</span>))</div><div class='output co'>#> [1] 7.207415e-07 9.991507e-01 8.486044e-04
#> </div><div class='input'><span class='co'># The sum of the elements of the inverse ilr is 1</span>
<span class='fu'>sum</span>(<span class='fu'>invilr</span>(<span class='fu'>c</span>(-<span class='fl'>10</span>, <span class='fl'>0</span>)))</div><div class='output co'>#> [1] 1
#> </div><div class='input'><span class='co'># This is why we do not need all elements of the inverse transformation to go back:</span>
<span class='no'>a</span> <span class='kw'><-</span> <span class='fu'>c</span>(<span class='fl'>0.1</span>, <span class='fl'>0.3</span>, <span class='fl'>0.5</span>)
<span class='no'>b</span> <span class='kw'><-</span> <span class='fu'>invilr</span>(<span class='no'>a</span>)
<span class='fu'>length</span>(<span class='no'>b</span>) <span class='co'># Four elements</span></div><div class='output co'>#> [1] 4
#> </div><div class='input'><span class='fu'>ilr</span>(<span class='fu'>c</span>(<span class='no'>b</span>[<span class='fl'>1</span>:<span class='fl'>3</span>], <span class='fl'>1</span> - <span class='fu'>sum</span>(<span class='no'>b</span>[<span class='fl'>1</span>:<span class='fl'>3</span>]))) <span class='co'># Gives c(0.1, 0.3, 0.5)</span></div><div class='output co'>#> [1] 0.1 0.3 0.5
#> </div></pre>
</div>
<div class="col-md-3">
<h2>Author</h2>
René Lehmann and Johannes Ranke
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