add sqinv() function

Author: victorpoughon

README.md

@@ -138,7 +138,6 @@ GitHub](https://github.com/sponsors/victorpoughon). Thank you ❤️
 
 ## Future work
 
-* Implement the "true inverse" of the square function: `sqinv(X) = sqrt(X) U -sqrt(X)`
 * Split full precision mode into two controls: input interpretation and display precision
 * Add `ans` variable (result of previous entry)
 * Add intersection operator or function

doc.md

@@ -7,7 +7,7 @@ Arithmetic](https://www.ime.usp.br/~montanhe/unions.pdf).
 An interval `[a, b]` represents the set of all numbers between and including a
 and b. An interval union: `[a, b] U [c, d]` is a disjoint set of intervals.
 
-Interval *union* arithmetic is an extension of regular interval arithmetic that
+Interval _union_ arithmetic is an extension of regular interval arithmetic that
 is vastly superior, mostly because it remains closed while supporting division
 by intervals containing zero:
 
@@ -96,6 +96,7 @@ bound. This design choice enables using arithmetic on interval bounds themselves
 |              Hull | `hull(A)`                | `➤ hull([1, 2] U [99, 100])`<br>`[1, 100]`              |
 |    Absolute value | `abs(A)`                 | `➤ abs([-10, 5])`<br>`[0, 10]`                          |
 |       Square root | `sqrt(A)`                | `➤ sqrt([9, 49])`<br>`[3, 7]`                           |
+|    Square Inverse | `sqinv(A)`               | `➤ sqinv([4, 64])`<br>`[-8, -2] U [2, 8]`               |
 | Natural logarithm | `log(A)`                 | `➤ log([0, 1])`<br>`[-∞, 0]`                            |
 |  Logarithm base 2 | `log2(A)`                | `➤ log2([64, 1024])`<br>`[6, 10]`                       |
 | Logarithm base 10 | `log10(A)`               | `➤ log10([0.0001, 1])`<br>`[-4, 0]`                     |
@@ -149,7 +150,6 @@ GitHub](https://github.com/sponsors/victorpoughon). Thank you&nbsp;❤️
 
 ## Future work
 
-* Implement the "true inverse" of the square function: `sqinv(X) = sqrt(X) U -sqrt(X)`
-* Split full precision mode into two controls: input interpretation and display precision
-* Add `ans` variable (result of previous entry)
-* Add intersection operator or function
+-   Split full precision mode into two controls: input interpretation and display precision
+-   Add `ans` variable (result of previous entry)
+-   Add intersection operator or function

index.html

@@ -207,54 +207,60 @@ <h2 id="supported-functions">Supported Functions</h2>
           style="text-align: left;"><code>➤ sqrt([9, 49])</code><br><code>[3, 7]</code></td>
           </tr>
           <tr class="odd">
+          <td style="text-align: right;">Square Inverse</td>
+          <td style="text-align: left;"><code>sqinv(A)</code></td>
+          <td
+          style="text-align: left;"><code>➤ sqinv([4, 64])</code><br><code>[-8, -2] U [2, 8]</code></td>
+          </tr>
+          <tr class="even">
           <td style="text-align: right;">Natural logarithm</td>
           <td style="text-align: left;"><code>log(A)</code></td>
           <td
           style="text-align: left;"><code>➤ log([0, 1])</code><br><code>[-∞, 0]</code></td>
           </tr>
-          <tr class="even">
+          <tr class="odd">
           <td style="text-align: right;">Logarithm base 2</td>
           <td style="text-align: left;"><code>log2(A)</code></td>
           <td
           style="text-align: left;"><code>➤ log2([64, 1024])</code><br><code>[6, 10]</code></td>
           </tr>
-          <tr class="odd">
+          <tr class="even">
           <td style="text-align: right;">Logarithm base 10</td>
           <td style="text-align: left;"><code>log10(A)</code></td>
           <td
           style="text-align: left;"><code>➤ log10([0.0001, 1])</code><br><code>[-4, 0]</code></td>
           </tr>
-          <tr class="even">
+          <tr class="odd">
           <td style="text-align: right;">Exponential</td>
           <td style="text-align: left;"><code>exp(A)</code></td>
           <td
           style="text-align: left;"><code>➤ exp([-∞, 0] U [1, 2])</code><br><code>[0, 1] U [2.718, 7.389]</code></td>
           </tr>
-          <tr class="odd">
+          <tr class="even">
           <td style="text-align: right;">Cosine</td>
           <td style="text-align: left;"><code>cos(A)</code></td>
           <td
           style="text-align: left;"><code>➤ cos([pi/3, pi])</code><br><code>[-1, 0.5]</code></td>
           </tr>
-          <tr class="even">
+          <tr class="odd">
           <td style="text-align: right;">Sine</td>
           <td style="text-align: left;"><code>sin(A)</code></td>
           <td
           style="text-align: left;"><code>➤ sin([pi/6, 5*pi/6])</code><br><code>[0.5, 1]</code></td>
           </tr>
-          <tr class="odd">
+          <tr class="even">
           <td style="text-align: right;">Tangent</td>
           <td style="text-align: left;"><code>tan(A)</code></td>
           <td
           style="text-align: left;"><code>➤ tan([pi/3, 2*pi/3])</code><br><code>[-∞, -1.732] U [1.732, +∞]</code></td>
           </tr>
-          <tr class="even">
+          <tr class="odd">
           <td style="text-align: right;">Minimum</td>
           <td style="text-align: left;"><code>min(A, B)</code></td>
           <td
           style="text-align: left;"><code>➤ min([1, 2], [0, 6])</code><br><code>[0, 2]</code></td>
           </tr>
-          <tr class="odd">
+          <tr class="even">
           <td style="text-align: right;">Maximum</td>
           <td style="text-align: left;"><code>max(A, B)</code></td>
           <td
@@ -307,6 +313,14 @@ <h2 id="open-source">Open Source</h2>
           you like my open-source work, please consider <a
           href="https://github.com/sponsors/victorpoughon">sponsoring me
           on GitHub</a>. Thank you ❤️</p>
+          <h2 id="future-work">Future work</h2>
+          <ul>
+          <li>Split full precision mode into two controls: input
+          interpretation and display precision</li>
+          <li>Add <code>ans</code> variable (result of previous
+          entry)</li>
+          <li>Add intersection operator or function</li>
+          </ul>
         </article>
         <script type="module" src="/src/main.ts"></script>
     </body>

src/functions.ts

@@ -64,6 +64,7 @@ const externalFunctions: Record<string, ExternalFunction> = {
     cos: fixedArity(1, nsf.ucos),
     sin: fixedArity(1, nsf.usin),
     tan: fixedArity(1, nsf.utan),
+    sqinv: fixedArity(1, nsf.sqinv),
 
     // Binary
     min: fixedArity(2, nsf.umin),