Amplitude 
<p><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle ~\rho ~}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mtext> </mtext><mi>ρ<!-- ρ --></mi><mtext> </mtext></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle ~\rho ~}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/79d0fbafed7b2c5bd6d84807f98778231d78a0a0" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.838ex; width:2.363ex; height:2.176ex;" alt="{\displaystyle ~\rho ~}"></span> and phase
<span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle ~\varphi ~}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mtext> </mtext><mi>φ<!-- φ --></mi><mtext> </mtext></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle ~\varphi ~}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/b5eabc11d968eeb1521c57400055c2052ffcd241" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.838ex; width:2.681ex; height:2.176ex;" alt="{\displaystyle ~\varphi ~}"></span> of !actorial <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f=\rho \exp({\rm {i}}\varphi )=(x+{\rm {i}}y)!=\Gamma (x+{\rm {i}}y+1)}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>f</mi><mo>=</mo><mi>ρ<!-- ρ --></mi><mi>exp</mi><mo>⁡<!-- ⁡ --></mo><mo stretchy="false">(</mo><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><mi mathvariant="normal">i</mi></mrow></mrow><mi>φ<!-- φ --></mi><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mi>x</mi><mo>+</mo><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><mi mathvariant="normal">i</mi></mrow></mrow><mi>y</mi><mo stretchy="false">)</mo><mo>!</mo><mo>=</mo><mi mathvariant="normal">Γ<!-- Γ --></mi><mo stretchy="false">(</mo><mi>x</mi><mo>+</mo><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><mi mathvariant="normal">i</mi></mrow></mrow><mi>y</mi><mo>+</mo><mn>1</mn><mo stretchy="false">)</mo></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle f=\rho \exp({\rm {i}}\varphi )=(x+{\rm {i}}y)!=\Gamma (x+{\rm {i}}y+1)}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fabb156fd90c8ab27bcae97104b3d6d7632d62d2" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.838ex; width:41.358ex; height:2.843ex;" alt="{\displaystyle f=\rho \exp({\rm {i}}\varphi )=(x+{\rm {i}}y)!=\Gamma (x+{\rm {i}}y+1)}"></span> in the complex <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x+{\rm {i}}y}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>x</mi><mo>+</mo><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><mi mathvariant="normal">i</mi></mrow></mrow><mi>y</mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle x+{\rm {i}}y}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/89de35bef2056ecde7f57e5afa6e6c7ca67c253e" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.671ex; width:5.972ex; height:2.509ex;" alt="{\displaystyle x+{\rm {i}}y}"></span> plane.
Several levels of constant modulus (amplitude) <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \rho ={\rm {const}}}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>ρ<!-- ρ --></mi><mo>=</mo><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><mi mathvariant="normal">c</mi><mi mathvariant="normal">o</mi><mi mathvariant="normal">n</mi><mi mathvariant="normal">s</mi><mi mathvariant="normal">t</mi></mrow></mrow></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle \rho ={\rm {const}}}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9bed86988a8f335056fc5ec12eee453a52f427fe" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.838ex; width:9.609ex; height:2.509ex;" alt="{\displaystyle \rho ={\rm {const}}}"></span> and constant phase <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \varphi ={\rm {const}}}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>φ<!-- φ --></mi><mo>=</mo><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><mi mathvariant="normal">c</mi><mi mathvariant="normal">o</mi><mi mathvariant="normal">n</mi><mi mathvariant="normal">s</mi><mi mathvariant="normal">t</mi></mrow></mrow></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle \varphi ={\rm {const}}}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/7dcb47b2fe161b3c63b2ad68fa944cfd4811eed9" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.838ex; width:9.927ex; height:2.509ex;" alt="{\displaystyle \varphi ={\rm {const}}}"></span> are shown. Set <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle ~f&lt;0~}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mtext> </mtext><mi>f</mi><mo>&lt;</mo><mn>0</mn><mtext> </mtext></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle ~f&lt;0~}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/cb6e39ca499f6b7cdd337a16ce03e234d47c1f73" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.671ex; width:6.701ex; height:2.509ex;" alt="{\displaystyle ~f&lt;0~}"></span> is shown with scratched line.
The grid covers range
<span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle ~-3\leq x\leq 3~}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mtext> </mtext><mo>−<!-- − --></mo><mn>3</mn><mo>≤<!-- ≤ --></mo><mi>x</mi><mo>≤<!-- ≤ --></mo><mn>3</mn><mtext> </mtext></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle ~-3\leq x\leq 3~}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/dddceeb80eaf017ae452ff85265e8ec4236ebfd9" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.505ex; width:13.853ex; height:2.343ex;" alt="{\displaystyle ~-3\leq x\leq 3~}"></span>,
<span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle ~-2\leq y\leq 2~}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mtext> </mtext><mo>−<!-- − --></mo><mn>2</mn><mo>≤<!-- ≤ --></mo><mi>y</mi><mo>≤<!-- ≤ --></mo><mn>2</mn><mtext> </mtext></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle ~-2\leq y\leq 2~}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d5826864814e5109fea4eb52fa271ebaa7226285" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.671ex; width:13.679ex; height:2.509ex;" alt="{\displaystyle ~-2\leq y\leq 2~}"></span>
</p>
with unit step.
<a href="//commons.wikimedia.org/wiki/User:Domitori" title="User:Domitori">Domitori</a> (Dmitrii Kouznetsov)
Attribution
<span class="int-own-work" lang="en">Own work</span>