傅里叶级数和傅里叶变换(从线性代数角度)
Stanford的公开课的笔记cos(x),sin(x), eixe^{ix} 的转换周期是2π2 \pi 的情况 f(x)=a0+∑1∞akcos(kx)+∑1∞bksin(kx) f(x)=a_0+\sum\limits_{1}^{\infty} {a_k}cos(kx)+\sum\limits_{1}^{\infty}{b_k}sin(kx) f(x)=∑0∞ckeikx f
