84 lines
2.4 KiB
C++
84 lines
2.4 KiB
C++
/*******************************************************************************
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* Copyright (c) 2015-2018 Skymind, Inc.
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*
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* This program and the accompanying materials are made available under the
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* terms of the Apache License, Version 2.0 which is available at
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* https://www.apache.org/licenses/LICENSE-2.0.
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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* SPDX-License-Identifier: Apache-2.0
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******************************************************************************/
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//
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// Created by Yurii Shyrma on 12.12.2017
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//
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#include<ops/declarable/helpers/zeta.h>
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#include <execution/Threads.h>
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namespace sd {
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namespace ops {
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namespace helpers {
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const int maxIter = 1000000; // max number of loop iterations
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//////////////////////////////////////////////////////////////////////////
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// slow implementation
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template <typename T>
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static FORCEINLINE T zetaScalarSlow(const T x, const T q) {
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const T precision = (T)1e-7; // function stops the calculation of series when next item is <= precision
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// if (x <= (T)1.)
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// throw("zeta function: x must be > 1 !");
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// if (q <= (T)0.)
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// throw("zeta function: q must be > 0 !");
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T item;
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T result = (T)0.;
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for(int i = 0; i < maxIter; ++i) {
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item = math::nd4j_pow((q + i),-x);
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result += item;
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if(item <= precision)
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break;
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}
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return result;
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}
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//////////////////////////////////////////////////////////////////////////
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// calculate the Hurwitz zeta function for arrays
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template <typename T>
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static void zeta_(sd::LaunchContext * context, const NDArray& x, const NDArray& q, NDArray &z) {
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//auto result = NDArray(&x, false, context);
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int xLen = x.lengthOf();
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auto func = PRAGMA_THREADS_FOR {
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for (auto i = start; i < stop; i++)
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z.p(i, zetaScalar<T>(x.e<T>(i), q.e<T>(i)));
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};
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samediff::Threads::parallel_for(func, 0, xLen);
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}
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void zeta(sd::LaunchContext * context, const NDArray& x, const NDArray& q, NDArray& z) {
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BUILD_SINGLE_SELECTOR(x.dataType(), zeta_, (context, x, q, z), FLOAT_TYPES);
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}
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BUILD_SINGLE_TEMPLATE(template void zeta_, (sd::LaunchContext * context, const NDArray& x, const NDArray& q, NDArray& z), FLOAT_TYPES);
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}
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}
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}
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